Burmese–Siamese War of 1765–1767

The Burmese–Siamese War of 1765–1767, also known as the War of the Second Fall of Ayutthaya (Thai: สงครามคราวเสียกรุงศรีอยุธยาครั้งที่สอง) was the second military conflict between Burma under the Konbaung dynasty and Ayutthaya Kingdom under the Siamese Ban Phlu Luang dynasty that lasted from 1765 until 1767; the war ended the 417-year-old Ayutthaya Kingdom. Burma under the new Konbaung dynasty emerged powerful in the mid-18th century. King Alaungpaya, the dynastic founder, led his Burmese forces of 40,000 men, and with his son Prince of Myedu as vanguard commander, invaded Siam in late 1759 to early 1760. The Burmese reached and attacked Ayutthaya in April 1760 but the arrival of rainy season and sudden illness of Alaungpaya prompted the Burmese to retreat. The traditional Siamese strategy of passive stand in the Ayutthaya citadel against Burmese besiegers worked for one last time, postponing the eventual fall of Ayutthaya for seven years. Alaungpaya died in May 1760 on his way from Siam back to Burma. Burmese invasion of Siam in 1760, in which the Burmese, particularly Prince Myedu, had an opportunity to learn about Siamese geography, strategy and tactics and to reflect about their own flaws in the campaign, served as the foundation of the next Burmese invasion in 1765–1767. Prince Myedu ascended the Burmese throne as King Hsinbyushin in late 1763. Hsinbyushin inherited military energy and prowess from his father Alaungpaya and was determined to accomplish his father's unfinished mission of conquering Ayutthaya. Burma sent forces to successfully conquer Lanna Chiang Mai in 1762–1763. In 1764, new Burmese king Hsinbyushin sent Ne Myo Thihapate with Burmese forces of 20,000 men to subjugate petty rebellions in Lanna and to proceed to invade Ayutthaya. Hsinbyushin also sent another 20,000 men under Maha Nawrahta to attack Siam from Tavoy in another direction, inflicting two-pronged pincer attack onto Ayutthaya. Siam, centered on the royal capital of Ayutthaya, was relatively defenseless against the militaristic Burmese. Due to long absence of external threats, the Siamese defense system had been largely in disuse since the late seventeenth century. Chronic manpower shortage also crippled Siamese defense. Nemyo Thihapate conquered Lao kingdoms of Luang Prabang and Vientiane in March 1765. With the Burmese conquests of Lanna and Laos, the Burmese took control and outflanked Siam's northern frontiers and also had access to vast manpower and other resources. In early 1765, Maha Nawrahta, from his base at Tavoy, sent his vanguard forces to invade and conquer Western Siamese provincial towns. Nemyo Thihapate, with his Burmese-Lanna contingents, descended onto Northern Siam in August 1765. Ayutthaya adopted hyper-centralized defensive strategy by calling provincial forces to defend Ayutthaya, focusing on protecting the royal city itself, leaving peripheral provincial cities less defended and at the mercy of Burmese invaders. Within the conquered Siamese provincial cities, Burmese commanders recruited local Siamese men to join their ranks. In October 1765, Maha Nawrahta, with his main Tavoy column, invaded Siamese Chao Phraya heartland. William Powney the British merchant, at the request of Ayutthayan court, engaged with Maha Nawrahta's Burmese forces in the Battle of Nonthaburi in December 1765 but the Burmese prevailed. Maha Nawrahta, with his Tavoy column coming from the west and Nemyo Thihapate with his Lanna column coming from the north, converged on Ayutthaya in January to February 1766, setting foot on the outskirts of Ayutthaya. Maha Nawrahta took position at Siguk to the west of Ayutthaya, while Nemyo Thihapate encamped at Paknam Prasop to the north of Ayutthaya. Siamese king Ekkathat sent Siamese defense forces in attempts to dislodge Burmese invaders from those places but failed. Siamese resistance group known as Bang Rachan emerged in February 1766 and ended in June, though not significantly impacting the course of the war but showcasing a side story of Siamese patriotic deeds that was later emphasized and celebrated by modern nationalistic Thai historiography of later centuries. For fourteen months, from February 1766 to April 1767, Ayutthaya endured the Burmese siege. Ayutthaya invoked the traditional strategy of passive stand inside of the Ayutthaya citadel, relying on two main defenses; the supposedly impregnable city wall fortified by French architects during the reign of King Narai and the arrival of wet rainy season. The Ayutthayans initially fared well as the foods and provisions were plentiful and the Siamese simply waited for the Burmese to leave but the Burmese besiegers did not intend to retreat. Learning from the previous invasion of 1760, King Hsinbyushin innovated and devised new strategy to overcome Siamese defenses. The Burmese would not leave during rainy season but would stand their grounds and endured wet swamps in order to pressure Ayutthaya into surrender. Burmese besiegers closed in and approached Ayutthaya in September 1766, with Nemyo Thihapate coming closer at Phosamton and Maha Nawrahta at Wat Phukhaothong temple. By late 1766, the situation became dire and desperate for Ayutthayan inhabitants as they ran out of food and resources, many simply surrendering themselves to the Burmese. Desperate, a Siamese military man of Teochew Chinese descent known as Phraya Tak gathered his Chinese–Siamese forces to break through the Burmese line to Eastern Siam in early January 1767, seeking for new position. Developing simultaneously was the Sino-Burmese War. Conflicts between Burma and Qing China over the frontier Shan States led to Yang Yingju the viceroy of Yungui sending Chinese Green Banner forces to directly invade Burma in October 1766. This prompted Burmese king Hsinbyushin, in January 1767, to command the Burmese besiegers in Ayutthaya to finish up the conquest of Ayutthaya in order to divert their forces to the Chinese front. Maha Nawrahta then escalated the siege by constructing twenty-seven forts surrounding Ayutthaya. In February to March 1767, Ayutthaya sent out volunteer Chinese and Portuguese Catholic fighters as the last line of defense, who were also defeated. Maha Nawrahta died from illness in March 1767, leaving his colleague Nemyo Thihapate to assume commands over the whole Burmese besieging forces. Nemyo Thihapate came up with a tactic to circumvent the Ayutthayan wall by digging underground tunnels into Ayutthaya. In early April 1767, the Burmese, through the tunnels, set fire to the roots of the wall, causing the northeastern portion of Ayutthayan wall to collapse, allowing the Burmese to eventually enter Ayutthaya. Ayutthaya, Siamese royal capital for four centuries, fell to the Burmese on 7 April 1767. What followed were violent scenes of the Burmese massacring of the inhabitants, burning of Siamese royal palaces, temples and vernacular structures and looting for treasures. Ekkathat, the last king of Ayutthaya, was either killed by a random gunshot or by starvation. 30,000 Siamese people, along with members of the fallen dynasty, craftsmen and cultural artifacts were all taken back to Burma. Nemyo Thihapate occupied the ruins of Ayutthaya for two months until his departure in June 1767, leaving only a small contingent under the Mon official Thugyi at Phosamton to oversee the short-lived Burmese occupation of Lower Central Siam, while the other part of the kingdom fragmented into a number of competing regional regimes. Burma diverted most of Ayutthaya occupation forces to the Chinese front, giving Siam a golden opportunity to resurge. Phraya Tak, the Siamese leader of Teochew Chinese heritage, who had earlier taken position in Eastern Siam, raised troops there to expel the Burmese and reconquered Ayutthaya-Thonburi area in November 1767. Ayutthaya was too ruinous and untenable to serve as Siam's capital so Phraya Tak, newly enthroned as King Taksin in December 1767, moved the Siamese royal seat to Thonburi south of Ayutthaya. Ayutthaya continued to exist as a second-class provincial towns, with its structural bricks dismantled for construction of Bangkok and its wealth looted by treasure hunters. After finishing the Chinese war in 1769, Hsinbyushin resumed the campaign to attack Siamese Thonburi kingdom in 1775–1776. However, Siam under the new regime was more resilient and competent at defense against Burmese invasions. Burmese invasion of Siam in 1785–1786 would be the last major large-scale Burmese invasion of Siam in history. Siam lost Tenaserim to Burma for perpetuity in 1765, becoming modern Tanintharyi region (Siam attempted to regain Tenasserim in 1792–1794 but failed.), in exchange for taking control of Lanna or modern Northern Thailand from Burma in 1775.

Background

Rise of the Konbaung dynasty

With the weakening of centuries-old Burmese Toungoo dynasty by mid-eighteenth century, the Mons in Lower Burma were able to break free and form their own kingdom. The Mons elected the monk Smim Htaw Buddhaketi to be their king of their Restored Hanthawaddy Kingdom in 1740. Smim Htaw, however, was deposed by a coup and replaced by his prime minister Binnya Dala in 1747 with Smim Htaw fleeing to Ayutthaya. Maha Damayaza Dipati, the last king of Toungoo dynasty, had authorities only in Upper Burma. Binnya Dala sent his brother Upayaza to lead Mon armies to conquer Upper Burma in 1751. Upayaza was able to seize Ava, the Burmese royal capital, in 1752, capturing Maha Damayaza Dipati to Pegu and ending the Toungoo dynasty. When Ava was falling to the Mon invaders, a local village chief of Moksobo named U Aung Zeiya rallied Burmese patriots to rise against the Mons. Aung Zeiya was enthroned as King Alaungpaya in 1752, founding the new Burmese Konbaung dynasty. Siam took hostile attitudes towards the Mon kingdom, leading to the Mons being preoccupied with possible Siamese threats from the east and allowing Alaungpaya to gather his Burmese forces and consolidate in Upper Burma. Alaungpaya's son Thado Minsaw (later Hsinbyushin) retook Ava from the Mons in 1754. Alaungpaya mobilized his Burmese forces to invade Lower Burma in the same year, capturing Prome in 1755 and attacking Syriam, where British and French traders had been residing, in 1756. Alaungpaya took Syriam in 1756 and killed French officials there for he was informed that the French had supported the Mons. Alaungpaya also seized two French ships containing field guns, thousands of flintlock muskets and other ammunitions – a great haul to Burmese armory. Alaungpaya then laid siege on Pegu, the Mon royal seat. The panicked Mon King Binnya Dala executed the former Burmese king Maha Damayaza Dipati, inadvertently giving Alaungpaya full legitimacy as the savior of Burmese nation. Alaungpaya seized Pegu in May 1757, thus unifying Upper and Lower Burma under him. Pegu was destroyed and the political administrative center of Lower Burma shifted from Pegu to Rangoon.

=== Internal developments of Ayutthaya === Burmese armies had not reached the outskirts of Ayutthaya since 1586 and, after King Naresuan's victory over the Battle of Nong Sarai in 1593, there had not been serious threatening Burmese invasions since then. In the aftermath of Siamese Revolution of 1688, Phetracha ascended the throne and founded his Ban Phlu Luang dynasty of the Late Ayutthaya Period, which was known for internal conflicts, including those in 1689, 1699, 1703 and 1733, owing to increasing powers of royal princes and nobility. Phetracha faced undaunting rebellions at regional centers of Nakhon Ratchasima (Khorat) and Nakhon Si Thammarat (Ligor) in 1699–1700, which took great efforts to quell. Siamese court of Late Ayutthaya, therefore, sought to decrease the powers of provincial governors. However, this reform became a failure and Ayutthayan court eventually lost effective control over its periphery. In pre-modern Siam, the military relied on conscripted levies as the backbone rather than professionally-trained personnel. In Late Ayutthaya Period, in early eighteenth century, Siam's rice export to Qing China grew. Siam became a prominent rice exporter into China through Teochew Chinese merchants. Siamese Phrai commoners of Central Siam, who cleared more lands and cultivated more rice for exports, became enriched through this economic prosperity and they became less willing to participate in military conscription and corvée levies. The Phrai evaded conscription through capitation taxes or commodity taxes and outright absence in order to partake in other more-profitable commercial activities. This led to overall decline of effective manpower control of Siamese Ayutthayan royal court over its own subjects. When Dowager Queen Yothathep died in 1735, there was not enough men to parade her funeral so King Borommakot had to relegate his own palace guards to join the procession. In 1742, the royal court managed to round up ten thousands of conscription evaders. Suppression of local governors means that they were less-armed and unable to provide frontline defenses against external invaders. Chronic manpower shortage undermined Siam's defense system. Government structure of Late Ayutthaya served to ensure internal stability and to prevent insurrections rather than to defend against invasions. Internal rebellions were more of realistic and immediate threats than Burmese incursions, which had become something of distant past, to Siam. Decline of manpower control and compromised defense system that would eventually lead to the Fall of Ayutthaya in 1767 left Siam vulnerable and resulted from Siamese court being unable to adapt and reform in response to changes.

==== Dynastic conflicts in Ayutthaya ==== Princely struggles began in 1755 when Prince Thammathibet, Borommakot's eldest son who had been the Wangna or Prince of the Front Palace and heir presumptive, arrested the servants of his half-brothers Chao Sam Krom or the Three Princes, who were sons of Borommakot born to secondary consorts rather than principal queens, for the princes' violation of ranks and honors. One of the Three Princes retaliated by informing Borommakot that Thammathibet had been in romantic relationships with two of the king's consorts. Borommakot punished Thammathibet by whipping with one hundred and eighty lashes of rattan blows, according to Siamese law. Thammathibet eventually succumbed to the wounds and died in 1756. In 1757, Prince Thepphiphit, other son of Borommakot, in concert with high ministers of Chatusadom, proposed his father the king to make Prince Uthumphon the new heir. Uthumphon initially refused the position due to the fact that he had an older brother Prince Ekkathat. However, Borommakot intentionally passed over Ekkathat, citing that Ekkathat was incompetent and sure to bring disaster to the kingdom. Borommakot forced his son Ekkathat to become a Buddhist monk to keep him away from politics and made his other son Uthumphon as the new Wangna in 1757. Borommakot died in May 1758. The Three Princes laid their claims to the throne against Uthumphon and had their armies break into royal palace to seize the guns. Five senior Buddhist prelates then beseeched the Three Princes to cease their belligerent actions. The Three Princes complied and went to visit Uthumphon to pay obeisance. However, Ekkathat secretly sent policemen to arrest the Three Princes and had them executed. Uthumphon ascended the throne as the new king but faced political pressure from his elder brother Ekkathat, who defiantly stayed in royal palace not returning to his temple despite being a Buddhist monk. Uthumphon eventually gave in and abdicated in June 1758 after merely a month on the throne. Ekkathat then eagerly left monkhood to take the throne as King Ekkathat the last king of Ayutthaya in 1758. Uthumphon became a monk at Wat Pradu Songtham Temple, earning him the epithet Khun Luang Hawat ('The King who seeks Temple'). In December 1758, Prince Thepphiphit, joined by other high-ranking ministers, came up with a conspiracy to overthrow Ekkathat in favor of Uthumphon. However, Uthumphon, not wanting the throne, chose to leak the seditious plot to Ekkathat himself. Ekkathat then had those conspiring ministers imprisoned and had his half-brother Thepphiphit board on a Dutch ship to be exiled to Sri Lankan Kingdom of Kandy. Phraya Phrakhlang the Minister of Trade was also implicated. Phrakhlang managed to pay a large sum of money to the king to avoid punishments. Ekkathat not only spared Phrakhlang but also created him Chaophraya Phrakhlang the Samuha Nayok or Prime Minister.

Burmese invasion of 1760

In early eighteenth century, the Tenasserim Coast was divided between Burma and Siam, with Tavoy belonging to Burma and Siam having Mergui and Tenasserim. In 1742, in the face of Mon insurrection, the Burmese governors of Martaban and Tavoy took refuge in Siam. Siam then took over the whole Tenasserim Coast. With Alaungpaya's conquest of Lower Burma in 1757, Tavoy returned to Burma. In 1758, Mon dissidents attacked Rangoon and Syriam but were repelled by the Burmese. The Mons rebels took a French vessel to flee and ended up in the Siamese port of Mergui. Burma demanded that Siam hand over the Mon rebels but Siamese authorities refused, saying that it was a mere French merchant ship. Burma then took this Siamese stance as being supportive of Mon insurrections against Burma. Realizing that Burmese eastern frontiers would never be pacified with Siam advocating the Mon cause, Alaungpaya decided to attack Siam. Tenasserim Coast then became Burmese–Siamese competing grounds.

Alaungpaya was also determined to conquer Siam as a part of Chakravartin concept of universal ruler to bring forth the new epoch of Maitreya Future Buddha. Alaungpaya and his armies left Shwebo in mid-1759 to Rangoon, where he was informed that the Siamese attacked Tavoy and Burmese trade ships were seized by the Siamese in Tavoy. Burmese vanguard, led by Minkhaung Nawrahta and the Prince of Myedu (Hsinbyushin) quickly took Mergui and Tenasserim in January 1760. King Ekathat sent an army under Phraya Yommaraj, with Phraya Phetchaburi Rueang as vanguard, to take position at the Singkhon Pass and another army under Phraya Rattanathibet as rearguard at Kuiburi. However, Phraya Yommaraj was defeated as the Burmese entered Western Siam. Phraya Rattanathibet sent his subordinate Khun Rong Palat Chu (ขุนรองปลัดชู) to face the Burmese at Wakhao Bay on the shore of Gulf of Siam near modern Prachuap Khiri Khan but was defeated by the Burmese in the Battle of Wakhao. Siamese generals, who were apparently inept compared to their battle-hardened Burmese counterparts, completely fell back to Ayutthaya. The Burmese vanguard took Kuiburi, Pranburi, Phetchaburi, Ratchaburi and Suphanburi in rapid succession. As the situation became critical, the panicked Ayutthayan court and people pleaded for the more-capable King Uthumphon to left monkhood to assume commands. Uthumphon sent Chaophraya Kalahom Khlongklaeb the Samuha Kalahom or Minister of Military with Siamese army to take position at Phakhai on the Talan River to the northwest of Ayutthaya. In the Battle of Talan, the Burmese vanguard was shelled by Siamese gunmen while crossing the river. Only when the main royal forces of Alaungpaya arrived in time to save the vanguard. Kalahom Khlongklaeb and other Siamese commanders were killed in battle. The Burmese reached the northwestern outskirts of Ayutthaya in April 1760 and took position at Bangban. Siamese boat people and foreign merchants moved to take refuge in the southern parts of the city moat. However, Burmese forces went to attack and massacre those refugees in the southern moat and plundering the area. Nicolaas Bang, the Dutch opperhoofd of Ayutthaya, died from drowning while trying to escape the Burmese. The Burmese mounted their cannons onto constructed towers to inflict fires onto Ayutthaya. The fires hit the Suriyat Amarin Palace, the royal residence of King Ekkathat, causing the palace spire to collapse. However, the time for the Burmese was running out as the wet rainy season approached that would turn Ayutthaya's suburbs into hostile swamps bred with diseases and discomfort. Thai chronicles stated that Alaungpaya was injured from an accidental cannon explosion, while Burmese chronicles stated that Alaungpaya fell ill with dysentery. Nevertheless, Alaungpaya had to turn back, retreating through the Maesot Pass and eventually died from illness at Kinwya village, halfway between Myawaddy and the Salween River, in May 1760. Siam was thus saved from Burmese conquest for one last time.

=== Interbellum events in Burma and Siam: 1760–1763 === After the demise of Alaungpaya, his eldest son Naungdawgyi succeeded to the throne in 1760 as the new Burmese king but Burma descended into a short period of internal upheaval. Minkhaung Nawrahta, while returning from Siamese campaign as the rearguard, passed through Toungoo where Thado Theinkathu the Prince of Toungoo, who was a brother of Alaungpaya, attempted to arrest him by orders from the new king Naungdawgyi. Minkhaung Nawrahta then arose in rebellion and seized Ava, only to be defeated and killed. Thado Theinkathu also soon took up arms against his nephew Naungdawgyi but was also suppressed in 1762. After these events, Burma became ready again for another round of military expeditions. Ayutthaya was saved from Burmese conquest for one last time after the retreat of Alaungpaya in May 1760 and political conflicts resumed. The more-capable Uthumphon, the former king, had left monkhood to lead commands against the Burmese invasion of 1760. In June 1760, Uthumphon visited his brother Ekkathat on one day but found Ekkathat having bare sword laying on his laps – a gesture of political aggression and enmity. Uthumphon then decided to leave royal palace and politics to become Buddhist monk at Wat Pradu temple again in mid-1760, this time permanently. In February 1761, a group of 600 Mon refugees took up arms and rebelled against Siam, taking position at Khao Nangbuat Mountain in modern Sarika, Nakhon Nayok to the east of Ayutthaya. Ekkathat sent royal forces of 2,000 men under Phraya Siharaj Decho to deal with Mon rebels. The Mons, armed with only melee sharpened wooden sticks, managed to repel Siamese forces. Ekkathat had to send another regiment of 2,000 men under Phraya Yommaraj and Phraya Phetchaburi Rueang in order to successfully put down the Mon rebellion. This showed how ineffective the Siamese military forces had become by 1761. Prince Thepphiphit, who had earlier been exiled to Sri Lanka after his failed rebellion in 1758, became involved in political conflicts in Sri Lanka. The Dutch conspired with native Sinhalese nobles, including the monks of Siam Nikaya sect, to assassinate King Kirti Sri Rajasinha of Kandy and to replace him with the Siamese prince Thepphiphit in 1760. However, Kirti Sri Rajasinha became aware of the plot and drove Thepphiphit out of Sri Lanka. Thepphiphit ended up returning to Siam, arriving at the port of Mergui in 1762. Ekkathat was shocked and enraged at the return of his fugitive half-brother and ordered his confinement in Tenasserim. Dutch–Siamese relations had been in deterioration state due to Dutch trade in Siam being unprofitable and the Siamese court forcing the Dutch to pay Recognitiegelden or procession fees to Siamese trade officials. The Dutch outright closed their factories at Ayutthaya, Ligor and left Siam in 1741. However, the Dutch decided to return and resume their trading post in Siam in 1748 for fear that the British would arrive and take over. During this low ebb of Dutch–Siamese relations, the British stepped in. In 1762, George Pigot the governor of Madras and President of East India Company sent a British merchant William Powney (known in Thai chronicles as "Alangkapuni") to Ayutthaya in order to renew relation with Siam. Powney presented King Ekkathat with a lion, an Arabian horse, an ostrich and proposed to establish a British outpost in Mergui. In late 1763, a Burmese governor named Udaungza rose up and seized power in Tavoy, killing the Konbaung-appointed Tavoy governor. Udaungza then proclaimed himself the governor of Tavoy and sent tributes to submit to Siam. Tavoy and Tenasserim Coast returned to Siamese rule again after this incident.

Burmese conquests of Lanna and Laos

Burmese conquest of Lanna (1763)

After the Burmese conquest of Lanna in 1558, Lanna or modern Northern Thailand had been mostly under Burmese rule. At the time when the Burmese Toungoo dynasty became weak, Ong Kham, the former Tai Lue king of Luang Prabang, expelled the Burmese from Chiang Mai in 1727 and made himself the King of Chiang Mai as an independent sovereign. Burma lost control over the region but Lanna became fragmented into individual princedoms. Upon victory of Alaungpaya over the Mons in 1757, Northern Thai Lanna rulers of Chiang Saen, Kengtung, Phrae and Nan sent congratulatory tributes to Alaungpaya at Pegu but Chiang Mai remained defiant, not sending tributes and Burma was yet to take actual control over Lanna. Alaungpaya still had to declare his intention to conquer Chiang Mai in September 1759 because Chiang Mai was not yet under Burmese control by then. Ong Kham of Chiang Mai died 1759, to be succeeded by his son Ong Chan. However, Ong Chan was deposed by his brother in 1761 who gave the throne to a Buddhist monk instead. In 1762, King Naungdawgyi of Burma recalled that the fifty-seven towns of Lanna used to be under Burmese suzerainty and sought to bring Lanna back under Burmese control. Naungdawgyi sent Burmese army under Abaya Kamani, with Minhla Thiri (later Maha Nawrahta) as second-in-command, with the forces of 7,500 men to conquer Chiang Mai in October 1762. Abaya Kamani reached Chiang Mai in December, taking position at Wat Kutao and laying siege on Chiang Mai. Chiang Mai requested supports from King Ekkathat of Ayutthaya. Chiang Mai persisted many months until August 1763 when Chiang Mai fell to the Burmese invaders. Ekkathat sent Chaophraya Phitsanulok Rueang the governor of Phitsanulok to bring Siamese forces to rescue Chiang Mai but he was too late as Chiang Mai had already fallen to the Burmese so the Siamese turned back. King Naungdawgyi died in December 1763 and was succeeded by his brother the Myedu Prince who became King Hsinbyushin. Abaya Kamani deported nearly the whole Northern Thai population of Chiang Mai, including the former king Ong Chan and Smim Htaw the former king of Pegu, to Burma in 1764. The new king Hsinbyushin appointed Abaya Kamani to be the Myowun or Burmese governor of Chiang Mai and elevated Minhla Thiri to become Maha Nawrahta the Myinwun or Commander of Cavalry. However, Lanna soon broke out in rebellion against Burma in 1764 under leaderships of Saen Khwang in Phayao and Nwe Mano in Lamphun. Hsinbyushin was determined to complete the unfinished mission of his father Alaungpaya in the conquest of Siam so initiated a grand campaign to accomplish his goal in 1764. He sent 20,000-men-strong army, under the command of Nemyo Thihapate, the Burmese commander who had a Lao (Lanna) mother according to a Thai chronicle composed in 1795, to conquer Lanna, Laos and then went on to conquer Siam. Nemyo Thihapate left for Lanna in February 1764, defeating Saen Khwang near Chiang Saen and Nwe Mano at Lamphun. Nemyo Thihapate also took Lampang, installing Chaikaew (father of Kawila) as the ruler of Lampang. After pacifying Lanna, as the rainy season arrived, Nemyo Thihapate and his Burmese forces rested and sheltered at Nan.

=== Burmese conquest of Laos (1765) === Since early eighteenth century, the Lao kingdom of Lanxang had fragmented into three separate kingdoms of Luang Prabang, Vientiane and Champasak. Lao kingdoms of Luang Prabang and Vientiane had been engaging in political rivalry. In October 1764, King Ong Boun of Vientiane wrote a letter to King Hsinbyushin, urging the Burmese to invade his rival Luang Prabang. After sheltering for wet season at Nan in 1764, Nemyo Thihapate and his Burmese army set off to conquer Luang Prabang. The Burmese left Nan in November 1764 to reach Luang Prabang. King Sotikakumman of Luang Prabang and his brother Prince Surinyavong led Lao army of 50,000 men to face the Burmese on the banks of Mekong. However, in the Battle of Mekong, the Lao were soundly defeated and had to retreat into the city. Nemyo Thihapate reminded his soldiers that the goal of this campaign was not only to conquer Lanna and Laos but also to conquer Ayutthaya so they should not waste much time and should take Luang Prabang with urgency. Luang Prabang fell to the Burmese in March 1765. Sotikakumman had to give away his daughter, other Lao noblewomen and servants to the Burmese court. His brother Surinyawong was also captured as prisoner-of-war and hostage. After the Burmese victory at Luang Prabang, King Ong Boun of Vientiane submitted his kingdom to Burmese rule. The Lao kingdoms of Luang Prabang and Vientiane (not including the Kingdom of Champasak) then became Burmese vassals in 1765 and would remain so until the Siamese conquest of Laos in 1778–1779. After the Luang Prabang campaign, Nemyo Thihapate and his army went to pacify Kengtung and then took the wet season shelter at Lampang, contemplating the invasion of Siam by the end of that year.

Burmese preparations

=== Cause of the war === At his ascension in 1764, the new Burmese king Hsinbyushin was determined to accomplish the unfinished mission of his father King Alaungpaya to conquer Ayutthaya. Hsinbyushin had wanted to continue the war with Siam since the end of the last war. The Burmese–Siamese War (1765–1767) was the continuation of the war of 1759–1760, the casus belli of which was a dispute over the control of the Tenasserim coast and its trade, and Siamese support for ethnic Mon rebels of the fallen restored Hanthawaddy Kingdom of Lower Burma. The 1760 war, which claimed the life of the dynasty founder King Alaungpaya, was inconclusive. Although Burma regained control of the upper Tenasserim coast to Tavoy, it achieved none of its other objectives. In the Burmese south, the Siamese readily provided shelter to the defeated ethnic Mon rebels.

=== Burmese strategy === As the deputy commander-in-chief in the 1760 war, Hsinbyushin used his firsthand experience to plan the next invasion. His general plan called for a pincer movement on the Siamese capital from the north and the south. The Burmese battle plan was greatly shaped by their experience in the 1759–1760 war. First, they would avoid a single pronged attack route along the narrow Gulf of Siam coastline, which they discovered could easily be clogged up by more numerous Siamese forces. In 1760, the Burmese were forced to spend nearly three months (January–March) fighting their way out of the coastline. This time, they planned a multi-pronged attack from all sides to stretch out the numerically superior Siamese defenses. Secondly, they would start the invasion early to maximize the dry-season campaign period. In the previous war, Alaungpaya started the invasion too late (in late December 1759/early January 1760). When the Burmese finally reached Ayutthaya in mid-April, they only had a little over a month left before the rainy season to take the city. This time, they elected to begin the invasion at the height of the rainy season. By starting the invasion early, the Burmese hoped their armies would be within a striking distance from Ayutthaya at the beginning of the dry season.

Burmese preparations

After sending Nemyo Thihapate to Lanna in late 1764, Hsinbyushin dispatched another army of 20,000 men led by Maha Nawrahta, the Myinwun or Commander of Cavalry, to Tavoy in December 1764 (8th waxing of Nadaw 1126 ME), with Nemyo Gonnarat and Tuyin Yanaunggyaw as seconds-in-command and with Metkya Bo and Teingya Minkhaung as vanguard. The Burmese artillery corps was led by a group of about 200 French soldiers who were captured in the Battle of Syriam in 1756 during the Burmese civil war of 1752–1757. After sending off his armies to attack Ayutthaya, King Hsinbyushin himself led the Burmese forces to attack Manipur in January 1765. King Chingthang Khomba or King Jaisingh of Manipur marched out to face the Burmese king in the Battle of Kakching in February but the Burmese prevailed, prompting the Manipur monarch to flee to Cachar, asking for aid from the Ahom kingdom. Hsinbyushin stayed in Manipur for about a month until his return to Burma as he appointed Prince Moirang, uncle and political enemy of Jaisingh, to be the puppet king of Manipur under Burmese domination. Hsinbyushin deported a great number of Meitei people back to Burma, recruiting Meitei horsemen as Cassay Horse units serving the Burmese army. Upon returning to Burma, Hsinbyushin realized that his royal capital of Shwebo, located at the northwestern corner of Burma, was unsuitable for governance so he moved the royal capital to Ava on 1 April 1765 (11th waxing of Tagu, 1127 ME). Burmese conquests of Lanna and Laos in 1762–1765 allowed Burma to access food and manpower resources that were later proven to be crucial to the Ayutthaya campaign. Ne Myo Thihapate was ordered to raise an army from the Shan States throughout 1764. By November, Ne Myo Thihapate commanded a 20,000-strong army at Kengtung, preparing to leave for Chiang Mai. As was customary, the Shan regiments were led by their own saophas (chiefs). (Not everyone was happy about the Burmese army's conscription drive, however. Some of the saophas of northern Shan states, which at the time paid dual tribute to Burma and China, fled to China, and complained to the Chinese emperor). Nemyo Thihapate rested his armies in Lampang for the rainy season of 1765, preparing for the upcoming invasion of Siam.

Burmese invasion of Western Siam

=== Burmese conquest of Tenasserim === Tenasserim Coast came under Siamese domination again in late 1763 due to defection of Udaungza, the self-proclaimed governor of Tavoy. Maha Nawrahta and his armies left Burma in December 1764, reaching Martaban. Maha Nawrahta sent his vanguard of 5,000 men to take Tavoy in January 1765. Udaungza took refuge in Mergui. Maha Nawrahta sent a ship to Mergui, asking for the surrender of Udaungza. When Siamese authorities did not comply, Maha Nawrahta then quickly took Mergui and Tenasserim on 11 January 1765, massacring the population who failed to escape. Ayutthaya received the news of the Burmese conquest of Tenasserim with consternation as the royal court prepared for the defense of the capital. In April 1765, King Hsinbyushin moved his royal seat to Ava, the traditional Burmese capital. He also reinforced Maha Nawrahta with additional forces of 10,000 men including;

Pegu regiment; 3,000 men, under Einda Yaza Martaban regiment; 3,000 men, under Binnya Sein including the newly-recruited forces from Tenasserim;

Tavoy regiment; 2,000 men, under the governor of Martaban Mergui and Tenasserim regiment; 2,000 men, under Lakyawdin This, combined with the original number of 20,000 men, made the total forces of 30,000 men under Maha Nawrahta. The Burmese army had now mobilized 50,000 men, including those in Lanna. (This likely represented the largest mobilization of the Burmese army since Bayinnaung's 1568–1569 invasion.)

=== Burmese invasion of Western Siam === Thai, French and Dutch sources state that the Burmese forces invaded Western Siam in early 1765. Udaungza the fugitive former governor of Tavoy fled from Tenasserim down south to Kra Isthmus to Kraburi. The Burmese were keen on chasing after Udaungza and then followed Udaungza to Kraburi, burning down the town. The Tavoy governor fled further to Phetchaburi, where Prince Thepphiphit also took refuge. The Burmese forces sacked and burnt down the Siamese towns of Chumphon, Pathio, Kuiburi and Pranburi on the way and then returned to Tavoy via the Singkhon Pass. King Ekkathat arranged for Prince Thepphiphit to be grounded in Chanthaburi and Udaungza to reside in Chonburi on Eastern Siamese Coast. The Siamese king then sent out forces to halt Burmese advances;

Chaophraya Phrakhlang the Samuha Nayok or Prime Minister, accompanied by Phraya Yommaraj and Phraya Tak, led the forces of 15,000 men including armored elephants and mounted cannons to deal with the Burmese at Phetchaburi and Ratchaburi. Chaophraya Nakhon Si Thammarat the governor of Nakhon Si Thammarat (Ligor) led Southern Siamese forces to defend the Singkhon Pass against possible Burmese incursion from Tenasserim. Phraya Kalahom the Samuha Kalahom of Minister of Military, led Siamese forces to the Three Pagodas Pass, where the Burmese did not come, showing the inaccuracy of the Siamese intelligence system. Phraya Phetchaburi Rueang the governor of Phetchaburi, led the Siamese army north to Sawankhalok to defend against the Burmese invasion from Lanna. Phra Phirenthorathep stationed his troops at Kanchanaburi. In May 1765, Maha Nawrahta at Tavoy sent his vanguard forces of 5,000 men under Metkya Bo and Teingya Minkhaung, passing through the Myitta Pass to attack Kanchanaburi. Phra Phirenthorathep at Kanchanaburi, with his 3,000 men, was defeated and retreated. The Burmese vanguard then quickly conquered Western Siamese cities. By this point, the Ayutthayan royal government had lost any control over its peripheral cities, which were left at the mercy of the Burmese. The Burmese invaders took a reconciliatory approach to these outlying Siamese towns. Towns that brought no resistance were spared from destruction and surrendered Siamese leaders were made to swear loyalty. Any cities that resisted and took up arms against Burmese invaders would face military punishment and subjugation. The main Siamese forces of Chaophraya Phrakhlang met with the Burmese vanguard at Ratchaburi, leading to the Battle of Ratchaburi. The Siamese in Ratchaburi resisted for many days. Siamese elephant mahouts intoxicated their elephants with alcohol in order to make them more aggressive, but one day this intoxication went too far as the elephants became uncontrollable, leading to Siamese defeat and Burmese capture of Ratchaburi. Western Siamese towns of Ratchaburi, Phetchaburi, Kanchanaburi and Chaiya all fell to the Burmese. Siamese people in these fallen cities fled into the jungles in large numbers as they were hunted down and captured by the invaders. After conquering Western Siam, the Burmese vanguard encamped at Kanchanaburi in modern Tha Maka district where the two rivers (Khwae Yai and Khwae Noi) met, while Maha Nawrahta himself was still in Tavoy. Maha Nawrahta also organized Western Siamese captives from Phetchaburi, Ratchaburi, Kanchanaburi, Suphanburi, Chaiya and Chumphon into regiments placed under the rearguard of Mingyi Kamani Sanda, the Wun of Pakhan. French and Dutch sources stated that all cities to the west of Ayutthaya had fallen under Burmese control by early 1765. Abraham Werndlij, the new Dutch opperhoofd of Ayutthaya, expressed his concerns that Siam was unable to do anything and left the Burmese to occupy Western Siam, which was the source of Dutch commodities including sappanwood and tin. The main reason for the quick fall of Kanchanaburi could be that the Burmese were battle-hardened. But it could also be that the Siamese command miscalculated where the Burmese main attack would come from, and had not sufficiently reinforced the fort to withstand a major attack. Judging by the Siamese chronicles' reporting of the main attack route, the Siamese command appeared to have believed that the main Burmese attack would come from the Gulf of Siam coastline, instead of the most obvious and shortest route via Kanchanaburi. The Siamese sources say that Maha Nawrahta's main invasion route came from southern Tenasserim, crossing the Tenasserim range at Chumphon and Phetchaburi. The path is totally different from the Kanchanaburi route reported by the Burmese chronicles. Historian Kyaw Thet specifically adds that the main attack route was via the Myitta Pass.

The Chumphon route is unlikely to have been the main attack route as it was even farther south than Alaungpaya's Kui Buri route. It means the Burmese would have had a longer route to go back up the Gulf of Siam coast. Without the element of surprise that Alaungpaya enjoyed in the 1760 war, the Burmese invasion force of 1765 would have had to fight more than three months it took Alaungpaya to break away from the coast. Yet, Maha Nawrahta's army was west of Ayutthaya by December. To be sure, the smaller Burmese army that took Tenasserim could have crossed over at Chumphon, and marched up the coast although the most southerly battles reported by the Burmese were at Ratchaburi and Phetchaburi, on the northern coast. At any rate, according to the Burmese sources, Chumphon was not the main attack route

=== Siamese preparations === As the Burmese had occupied all of Western Siam by early 1765 encamping at Kanchanaburi, King Ekkathat organized Siamese forces of 15,000 to 16,000 men to spread out to defend against Burmese invaders in June 1765;

Chaophraya Nakhon Si Thammarat, the governor of Ligor (which was the principal city of Southern Siam), stationed his Southern Siamese troops of 1,000 men at Bang Bamru just to the south of Burmese-occupied Ratchaburi. Chaophraya Phitsanulok Rueang, the governor of Phitsanulok (which was the principal city of Northern Siam), took position of his Northern Siamese forces at Wat Phukhaothong temple to the northwest of Ayutthaya. Phraya Nakhon Ratchasima, the governor of Nakhon Ratchasima, led his Khorat troops to take position at Wat Chedi Daeng temple to the north of Ayutthaya. Phraya Rattanathibet, the Minister of Palace Affairs, led the Khorat forces of 4,000 men to take position at Thonburi to the south of Ayutthaya to prevent Burmese riverine advances through the Chao Phraya River. An iron chain was erected across the river to obstruct the Burmese fleet. Phraya Yommaraj, the Head of Police Bureau, with 2,000 men stationed at Nonthaburi.

Wet Season Campaign (August–October 1765)

=== Southern Front: Battle of Thonburi === By mid-1765, Maha Nawrahta the commander of the Burmese Tavoy column had still been in Tavoy, while his vanguard had already encamping at Kanchanaburi. In August 1765, the Burmese vanguard at Kanchanaburi, led by Metkya Bo, attacked and repelled the Southern Siamese forces under the governor of Ligor at Bang Bamru. Suffering the defeat, the Ligor governor was then charged with incompetency, arrested and imprisoned in Ayutthaya. Metkya Bo and Teingya Minkhaung led their Burmese vanguard to proceed to attack Thonburi. The panicked Siamese commander Phraya Rattanathibet abandoned his position and retreated with his Khorat regiment technically dispersed. The Burmese vanguard seized the French-constructed Wichaiyen Fort at Bangkok. French Catholic seminary and Dutch trade factory at Thonburi were also burnt down and destroyed. After successful capture of Thonburi, the Burmese vanguard then returned to the position at Kanchanaburi.

Northern Front: Burmese invasion of Northern Siam

After subjugating Lanna and Laos, Nemyo Thihapate and his Burmese forces took rainy season shelter in Lampang. Conquest of Lanna and Laos allowed the Burmese to access vast manpower and other resources to be utilized in their invasion of Siam from the north. In mid-1765, Nemyo Thihapate recruited local Lanna and Lao men into regiments, adding to the total of 43,000 men, 400 elephants, 1,200 horses and 300 riverine vessels alongside the existing Burmese forces; The Lanna (Yun) regiments, under the command of Thado Mindin (who later became the Burmese governor of Chiang Mai in 1769), composing of 12,000 men, 200 elephants and 700 horses, were recruited from Chiang Mai, Lampang, Lamphun, Chiang Saen, Nan, Phrae, Chiang Rai, Phayao, Chiang Khong, Mong Hsat, Mongpu, Kenglat and Mongnai. The Lanxang (Linzin) regiments, under the command of Thiri Yazathingyan, composing of 8,000 men, 100 elephants and 300 horses, were recruited from Luang Prabang, Vientiane, Muang La, Mong Yawng and Mong Hang. Burmese riparian fleet, composing of 10,000 men and 300 boats under leadership of Tuyin Yamagyaw. Nemyo Thihapate and his Burmese-Lanna-Lao forces left Lampang on 23 August 1765 (8th waxing of Tawthalin 1127 ME) at the height of the rainy season down the Wang River to attack Hua Mueang Nuea or Northern Siam. The reason for the earlier start of the northern army was that it was much farther away from Ayutthaya than its southern counterparts. Still the strategy did not work as planned. Like Maha Nawrahta, Nemyo Thihapate sent his vanguard forces of 5,000 men under Satpagyon Bo to do the initial conquests. Satpagyon Bo met Phraya Phetchaburi Rueang the commander of northern Siamese defense forces at Sawankhalok, leading to the Battle of Sawankhalok. Sawankhalok resisted for many days but was eventually conquered by the Burmese commander Satpagyon Bo and Phraya Phetchaburi Rueang had to retreat south to Chainat. Siamese initial defeat at Sawankhalok left the whole Northern Siam vulnerable to Burmese conquests. After Sawankhalok, Satpagyon Bo attacked Sukhothai and Tak, where the governor Phraya Tak was called to Ayutthaya leaving little defense to the town. Tak offered resistance but eventually fell to the Burmese commander Satpagyon Bo. After Tak, Satpagyon Bo proceeded to attack Kamphaeng Phet, which offered no resistances. Burmese invading forces in the northern front implemented in the same policy as in the southwestern front in regard to peripheral Siamese cities, in which the cities that surrendered would be spared from destruction but any cities that resisted would face punishment. The northern army's advance was greatly slowed by the rainy weather and the "petty chiefs" who put up a fight, forcing Thihapate to storm town after town. Nonetheless, the Burmese vangaurd fought the way down the Wang, finally taking Tak and Kamphaeng Phet by the end of the rainy season.

Dry Season Campaign (October 1765 – January 1766)

=== Southern Front: Battle of Nonthaburi === Maha Nawrahta himself marched his main forces from Tavoy to Kanchanaburi, leaving Tavoy on 23 October 1765 (10th waxing of Tazaungmon 1127 ME) in three directions. He had 20,000 to 30,000 under his command. (The Burmese sources say 30,000 men including 2000 horses and 200 elephants but G E Harvey gives the actual invasion force as 20,000. At least part of the difference could be explained by the rearguard who stayed behind to defend the Tenasserim coast). A small army invaded by the Three Pagodas Pass towards Suphan Buri. Another small army invaded down the Tenasserim coast towards Mergui (Myeik) and Tenasserim (Tanintharyi) town. However, the main thrust of his attack was at Kanchanaburi. His 20,000-strong main southern army invaded via the Myitta Pass. (It was also the same route the Japanese used in 1942 to invade Burma from Thailand.) Kanchanaburi fell with little resistance. In 1765, the British trader William Powney (called Alangkapuni in Thai sources) sailed his merchant ship to Ayutthaya, bringing Indian textiles to sell. However, his business was unsuccessful apparently because Siam had been in the middle of warfare and no one was bothered to buy luxurious goods. Powney instead was caught in the indigenous warfare as King Ekkathat, through his minister Chaophraya Phrakhlang, requested for the aid from Powney to defend against the Burmese invasion, in which Powney agreed on conditions that the Siamese court should provide him with adequate resources. Powney then sailed downstream from Ayutthaya and anchored his brigantine at Thonburi to halt Burmese advances. Abraham Werndlij, the Dutch opperhoofd, was very concerned about the prospect that Ayutthaya royal city would again be attacked by the Burmese, as fresh memory of the death of the previous opperhoofd in 1760 and the loss of commodity goods were still looming. In October 1765, a Dutch diplomatic ship arrived in Ayutthaya from Batavia, giving instructions to Werndlij to secretly close down and abandon the Dutch factory in Ayutthaya to escape Burmese attacks. Werndlij, with the ship carrying as many Dutch goods as possible, hurriedly left Ayutthaya on 28 October. After resting at the mouth of Chao Phraya River, Werndlij and his Dutch ship left Siam in early November 1765, ending Ayutthaya–Dutch relations. In December 1765, Maha Nawrahta at Kanchanaburi sent his vanguard under Metkya Bo to occupy Thonburi again, reaching Thonburi on 24 December. Metkya Bo took position at the Wichayen Fort in Bangkok, mounting his cannon to fire on Powney's brigantine warship at Thonburi, prompting Powney to retreat to Nonthaburi. The Siamese commander Phraya Yommaraj at Nonthaburi abandoned his position and retreated in panic, leaving Powney alone to fight the Burmese. Metkya Bo then proceeded to take position and encamp at Wat Khema Phitaram temple in Nonthaburi, about 60 km south of Ayutthaya, on both banks of the Chao Phraya River. Powney requested for more firearms and ammunition from the Siamese royal court. Ayutthayan court agreed to send supplies but Powney had to deposit his trade goods in the Phra Klang Sinkha or Royal Warehouse in exchange – the condition that Powney only reluctantly complied. The Burmese finally faced a serious Siamese defensive line guarding the route to the capital. On one night, Powney and his Siamese allies sailed down to make a joint land-naval attack on the Burmese garrison at Nonthaburi by surprise, leading to the Battle of Nonthaburi in December 1765 – the first major battle of the southern theatre. The Burmese suffered losses but also feigned retreat. The unsuspecting Siamese soldiers along with a number of British traders entered Nonthaburi without caution, where they were ambushed and routed by the Burmese. The Burmese put the severed head of a British supercargo on a pike for display. Defeated, Powney pressed for more guns, boats and personnel from Ayutthaya through Chaophraya Phrakhlang but this time his demands were not met due to the Siamese court being low in resources and did not fully trust Powney. Powney was dissatisfied about Siam not complying to his demands so he decided to turn against Siam. Powney abandoned his position and eventually left Siam, leaving his cargo behind in Ayutthaya and plundering six Chinese–Siamese junks on the way.

Northern Front: Battle of Sukhothai

Chaophraya Phitsanulok Rueang, who had been in command of Northern Siamese regiment at Wat Phukhaothong temple in Ayutthaya, in the middle of warfare, gained permission from King Ekkathat to return to Phitsanulok to attend his mother's funeral, leaving his subordinate Luang Kosa to be in charge. In October 1765, the Burmese vanguard under Satpagyon Bo attacked Sukhothai and took the city. The Siamese had to initially abandon their city and returned to lay siege on the Burmese-occupied Sukhothai, leading to the Battle of Sukhothai. Chaophraya Phitsanulok brought forces from his base in Phitsanulok to participate in the siege of Sukhothai. In November 1765, Prince Chaofa Chit, who had been a political prisoner inside of the Ayutthayan palace, broke free and went to visit Uthumphon the temple king at Wat Pradu Songtham temple with the help of Luang Kosa of Phitsanulok. This political incident put the Siamese royal court in commotion. Luang Kosa then took Prince Chit north to Phitsanulok, where Chaophraya Phitsanulok the governor was absent and away fighting the Burmese at Sukhothai. Prince Chit then decided to seize power and establish himself in Phitsanulok, fortifying himself against King Ekkathat. Lady Chuengchiang, wife of Chaophraya Phitsanulok, escaped in a small boat to inform her husband at Sukhothai about the coup of Prince Chit in Phitsanulok. Chaophraya Phitsanulok was so enraged that he decided to abandon his campaign in Sukhothai and returned to Phitsanulok, bringing his forces to subjugate Prince Chit. Battle ensued between Chaophraya Phitsanulok and Prince Chit in Phitsanulok and this distraction allowed the Burmese to proceed. Eventually, Chaophraya Phitsanulok was able to retake his city, capturing the fugitive Prince Chit. Chaophraya Phitsanulok then had Prince Chit executed by drowning. Ne Myo Thihapate's northern army was stuck in northern Siam although the pace of his advance had improved considerably since the end of the rainy season. After taking Kamphaeng Phet, Thihapate turned northeast, and captured the main northern cities of Sukhothai and Phitsanulok. Burmese chronicles states that the Burmese army took Phitsanulok by force, occupying Phitsanulok as the base for months. However, Thai chronicles describes that Nemyo Thihapate went directly from Sukhothai to Kamphaeng Phet in January 1766 without taking Phitsanulok, presuming that Chaophraya Phitsanulok retained his position in Phitsanulok as he would later survive to become one of the regional regime leaders after the Fall of Ayutthaya. At Phitsanulok, Nemyo Thihapate paused to refill the ranks because in about 4 months, he had already lost many men to the grueling campaign and to "preventable diseases". The local chiefs were made to drink the water of allegiance and provide conscripts to the Burmese army. (Outside Ayutthaya, Maha Nawrahta too was collecting local levies.) While the Burmese refilled their ranks, the Siamese command belatedly sent another army to retake Phitsanulok. But the Siamese army was driven back with heavy losses. It was the last major stand by the Siamese in the north. The Siamese defense collapsed afterwards. Nemyo Thihapate sent his two commanders Thiri Nanda Thingyan and Kyawgaung Kyawthu to finish up the remaining Northern Siamese towns of Phichai, Phichit, Nakhon Sawan and Ang Thong. The Burmese army moved by boat down the Nan River, taking Phichai, Phichit, Nakhon Sawan, and down the Chao Phraya, taking Ang Thong. Captured Siamese cannons and firearms were sent to Burmese-held Chiang Mai to be stocked. Nemyo Thihapate also organized Northern Siamese men from Tak, Kamphaeng Phet, Sawankhalok, Sukhothai, Phitsanulok, Phichai, Phichit, Nakhon Sawan and Ang Thong into new regiments under the vanguard command of Nanda Udein Kyawdin.

=== Western Front: Battle of Siguk === In early 1766, King Ekkathat sent Phraya Phollathep the Minister of Agriculture to lead Siamese forces, which the Burmese chronicles describes as having up to 60,000 men with 500 elephants and 500 cannons, to station at Siguk (Thigok in Burmese, in modern Nam Tao, Bang Ban, Ayutthaya) about ten kilometers to the west of Ayutthaya. Maha Nawrahta at Kanchanaburi proceeded towards Ayutthaya in January 1766, dividing his armies into two routes;

The first route, the land armies taken by Maha Nawrahta himself, would march through Suphanburi to approach Ayutthaya from the west. The second route, the riparian fleet led by Mingyi Kamani Sanda, sailed through Thonburi and Nonthaburi on the Chao Phraya River, approaching Ayutthaya from the south. Maha Nawrahta and his main forces met the Siamese force of 60,000 men under the command of Chaophraya Phollathep at Siguk to the west of Ayutthaya, leading to the Battle of Siguk. Outnumbered 3 to 1, the more experienced Burmese army nonetheless routed the much larger Siamese army, which according to the Burmese, was "chopped to pieces", forcing the remaining Siamese troops to retreat to the capital. Maha Nawrahta had now arrived at Ayutthaya as planned, in record time. ("It took Alaungpaya's 40,000 men about three and a half months to arrive at Ayutthaya in 1760 whereas it took Maha Nawrahta's 20,000 plus army just about two months"). But he pulled back to the northwest of the city because he did not see Thihapate's northern army, and because he did not want to take on another major battle with his depleted army. He used the hiatus to refill the ranks with Siamese conscripts.

=== Burmese Approach onto Ayutthaya === Mingyi Kamani Sanda and his fleet proceeded through the Chao Phraya River and took position at Bangsai (in modern Bang Pa-in district), about five kilometers to the south of Ayutthaya where the main Ayutthayan waterway checkpoint stood. After the victorious Battle of Siguk, Maha Nawrahta informed King Hsinbyushin at Ava that he had conquered all cities to the west of Ayutthaya and had already taken position in the outskirts of Ayutthaya, waiting for Nemyo Thihapate to join from the north. King Hsinbyushin appointed Mingyi Manya to be the new governor of Tavoy to replace Udaungza, signifying long-term Burmese control of Tavoy. The Burmese king also sent a Mon regiment of 2,000 men under the command of Binnya Sein to join as an additional force. From Ang Thong, Nemyo Thihapate marched his army through the old route of Chao Phraya River that would become modern Khlong Bangkaeo canal from Ang Thong to Ayutthaya (Old route of Chao Phraya River was inadvertently diverted through a digging of a new canal from Ang Thong to Pamok. The old route gradually dried out in favor of the new route and became a smaller Bang Kaeo canal by Early Bangkok Period.). Nemyo Thihapate reached the environs of Ayutthaya on 20 January 1766 (5th waxing of Tabodwe 1127 ME), making contact with Maha Nawrahta's army. Nemyo Thihapate took position at Paknam Prasop (Panan Pathok in Burmese, modern Bang Pahan district), about seven kilometers to the north of Ayutthaya. By January 1766, all of the main Burmese forces, including both Tavoy and Chiang Mai columns, approached Ayutthaya in three directions;

Nemyo Thihapate, with his Burmese-Lanna-Lao forces of 20,000 men, encamped at Paknam Prasop to the north of Ayutthaya. Maha Nawrahta, with his 20,000–30,000 men, encamped at Siguk to the west of Ayutthaya. Mingyi Kamani Sanda stationed his fleet at Bangsai to the south of Ayutthaya, under the command of Maha Nawrahta. He was joined by the Mon regiment of Binnya Sein.