Reestablishment of Siamese AuthorityIn 1767, after dominating southeast Asia for almost 400 years, the Ayutthaya kingdom was destroyed. The royal palace and the city were burnt to the ground. The territory was occupied by the Burmese army and local leaders declared themselves overlords including the lords of Sakwangburi, Pimai, Chanthaburi, and Nakhon Si Thammarat. Chao Tak, a nobleman of Chinese descent and a capable military leader, made himself a lords and staged the legendary sack of Chanthaburi. Based at Chanthaburi, Chao Tak raised up the troops and resources and marched a fleet to the mouth of Chao Phraya taking Thonburi fort. In the same year, Chao Tak was able to retake Ayutthaya from the Burmese only seven months after the fall of the city.
Upon Siamese independence, Hsinbyushin of Burma ordered the ruler of Tavoy to invade Siam. The Burmese armies arrived through Sai Yok and laid siege on the Bang Kung camp - the camp for Taksin's Chinese troops - in modern Samut Songkhram Province. Taksin hurriedly sent one of his generals Boonma to command the fleet to Bang Kung to relieve the siege. Siamese armies encircled the Burmese siege and defeated them.
Ayutthaya, the center of Siamese authority for hundreds of years, was so devastated that it could not be used as a government center. Tak founded the new city of Thonburi Sri Mahasamut on the west bank of Chao Phraya river. The construction took place for about a year and Tak crowned himself in late 1768 as King Sanpet but he was known to people as King Taksin - a combination of his title and personal name. Taksin crowned himself as a King of Ayutthaya to signify the continuation to ancient glories.
 Reunification and ExpansionThere were still local warlords competing for Siam. Taksin marched first in 1768 to Pitsanulok to subjugate the Lord of Pitsanulok who ruled over Upper Chao Phraya Basin. Taksin was injured during the campaign and had to retreat. The war readily weakened Pitsanulok and then it was in turn subjugated by the Lord of Sakwangburi. The same year Taksin sent Thong Duang and Boonma to tame the Prince Theppipit - the ruler of Phimai to the north of Nakhon Ratchasima on the Khorat Plateau. The prince was a son of Borommakot and was defeated by Thonburi armies. Theppipit fled to Vientiene but was captured and then executed.
In 1769, Taksin sent Phraya Chakri south to subjugate the Lord of Nakorn Si Thammarat. The lord fled to Pattani but was returned to Taksin, who reinstalled him back as the ruler of Nakorn Si Thammarat under Taksin's governance.
Prince Ang Non the Uparaja of Cambodia fled to Thonburi in 1769 after his conflicts with King Narairaja for Siamese supports. Taksin then took this opportunity to request tributary from Cambodia, which Narairaja refused. Taksin sent Phraya Abhay Ronnarit and Phraya Anuchit Racha to subjugate Cambodia, taking Siemreap and Battambang. But Taksin's absence from the capital (in wars with Nakorn Si Thammarat) shook the political stability and the two generals decided to retreat to Thonburi.
By this time, the only rival to Thonburi authority was the Sakwangburi lordship led by the powerful monk Chao Phra Faang. Chao Phra Faang’s domain encompassed the northernmost territories bordering Lanna to Nakhon Sawan to the south as the result of annexation of Pitsanulok lordship in 1768. In 1770,Chao Phra Faang sent reinforcements southwards reaching Chainat. Taksin perceived this action as threats and decided to invade Sakwangburi beforehand. The royal fleet marched upstream the Chao Phraya River and took Pitsanulok with ease. Taksin then divided the armies into the east one led by Boonma and the west one led by Phraya Pichai to be joined at Sakwangburi. Sakwangburi quickly fell after three days and Chao Phra Faang went lost.
Taksin stayed at Pitsanulok to oversee the census and levy of northern population. He appointed Boonma to Chao Phraya Surasi as the governor of Pitsanulok and all northern cities and Phraya Abhay Ronnarit to Chao Phraya Chakri the chancellor.
Later in 1771, Taksin decided to finish off the Cambodian campaign by assigning Chao Phraya Chakri command of land forces with Prince Ang Non and Taksin himself went by fleet. The Siamese took various Cambodian cities and drove Narairaja out of the throne. Ang Non was installed as Reamraja and Narairaja became the Uparaja with the Cambodian court paying tribute to Thonburi.
 Wars with BurmaTaksin had consolidated the old Siamese kingdom with new base at Thonburi. However, the Burmese were still ready to wage massive wars to bring the Siamese down again. From their base at Chiang Mai, they invaded Sawankalok in 1770 but the Siamese were able to repel. This realized Taksin the importance of Lanna as the base of resources for the Burmese to attack northern territories. If Lanna was brought under Siamese control then the Burmese threats would by annihilated.
At the time Lanna, centered on Chiang Mai, was ruled by a Burmese general Paw Myunguaun. He was the general who led the invasion of Sawankalok in 1770 but was countered by Chao Phraya Surasi’s armies from Pitsanulok. In the same year, the Siamese pioneered a little invasion of Chiang Mai and failed to gain any fruitful results.
In 1772, Paw Thupla, another Burmese general who had been in wars in Laos, headed west and attack Pichai and Uttaradit. The armies of Pitsanulok once again repelled the Burmese invasions. They came again in 1773 and this time Phraya Pichai made his legendary sword break.
In 1774, Taksin ordered Chao Phrya Chakri and Chao Phraya Surasi to invade Chiang Mai. After nearly 300 years of Burmese rule, Lanna passed to the Siamese hands. The two Chao Phrayas were able to take Chiang Mai with the help of local insurgents against Burma and Taksin appointed them the local rulers: Phraya Chabaan as Phraya Vichianprakarn the Lord of Chiangmai, Phraya Kawila as the Lord of Lampang, and Phraya Vaiwongsa as Lord of Lampoon. All the lordships paid tribute to Thonburi. Paw Myunguaun and the Burmese authority retreated to Chiang Saen.
During Taksin’s northern campaigns, the Burmese armies took the opportunity to invade Thonburi through Ta Din Daeng. The Burmese encamped at Bangkaew but were surrounded by the Siamese armies commanded by Taksin. For more than a month the Burmese had been locked in the siege and thousand of them died. Another thousand became captives to the Siamese.
In 1776 there came the hugest invasion of the Burmese led by Maha Thiha Thura. Instead of dividing the forces invading through various ways, Maha Thiha Thura amassed the troop of 30,000 as a whole directly towards Pitsanulok whose inhabitants were only 10,000 in number. Paw Thupla and Paw Myunguaun from Chiang Saen attempted to retake Chiang Mai but were halted by the two Chao Phrayas, who after Chiang Mai hurried back to Pitsanulok to defend the city. The engagements occurred near Pitsanulok.
Maha Thiha Thura directed the troops at Pitsanulok so immensely that the Siamese were about to fall. He cut down the supply lines and attacked the royal army. The two Chao Phrayas decided to abandon Pitsanulok. The Burmese entered the city with victory but all went dead due to the death of Hsinbyushin the Burmese king the same year. They had to retreat.
After the death of the Burmese king Hsinbyushin the Burmese were plunged in their own dynastic struggles. In 1776, the new monarch Singusa sent Maha Thiha Thura to invade Lanna again with such a huge army that Lord Vichianprakarn of Chiang Mai had to abandon the city. Chao Phraya Surasi and Lord Kawila of Lampang retook Chiang Mai from the Burmese but decided to left the city abandoned as there was no population to fill the city. No further Burmese invasions came as Singu staged his dynastic purges on the princes and Maha Thiha Thura himself.
 Expansions and economic problemsIn 1776, a governor of Nangrong (modern Nakhon Nayok) had a row with the governor of Nakhon Ratchasima the head city of the region. The governor then sought supports from King Sayakumane of Champasak. This became a casus bellum for Taksin to sent Chao Phraya Chakri to conquer Champasak. King Sayakumane fled but was captured and detained in Thonburi for two years until he was sent to rule his kingdom again in 1780 paying tribute to Thonburi. The Champasak campaign earned Chakri the title Somdet Chao Phraya Maha Kasatseuk. Taksin invented the title Somdet Chao Phraya for a mandarin with equal honor as a royalty.
In 1778, a Laotian mandarin named Phra Wo sought Siamese supports against King Bunsan of Vientiene but was killed by the Laotian king. Taksin then dispatched the troops in 1779 led by the two famous brothers commanders, Phraya Chakri and his brother, Phraya Surasi to subjugate Vientiene. At the same time King Suriyavong of Luang Prabang submitted himself to Thonburi and joined the invasion of Vientiene. King Bunsan fled and hid in the forests but later gave up himself to the Siamese. The Vientiene royal family was deported to Thonburi as hostages. Thonburi forces took two valuable Buddha images, the symbolic icons of Vientiane – the Emerald Buddha and Phra Bang to Thonburi. Then all of the three Laotian kingdoms became Siamese tributaries and remained under Siamese rule for another hundred years.
Years of warfare and the Burmese invasions prevented any peasants to engage in agricultural activities. Majority of people had been deported to Burma in the fall of Ayutthaya in 1767 and the lack of manpower became the source of problems. Taksin had tried his best to encourage people to come out of forest hidings and promote farming. He promulgated the Conscription Tattooing in 1773 to left a permanent mark on commoners' bodies, preventing them from fleeing or moving. The practice continued well into Rattanakosin times until the abolition of levy itself by King Chulalongkorn later. As Taksin was from a Chinese merchant family, he sold his both royal and familial properties and belongings to subsidize the production by giving money off to people. This proved to be a temporary relief for such an economic decline. Nevertheless, the Siamese economy after the catastrophes needed time to rehabilitate.
Taksin himself also commissioned trade missions to the neighboring countries to bring Siam back to outside world, mainly with China. He dispatched several missions with tributes to the Qing in 1781 to resume diplomatic and commercial relationships.
 Political and economic troublesThonburi began forming its society. Taksin gathered resources by wars and dealts with Chinese merchants. Major groups of people in Thonburi were local Thais, phrai,or 'commoners', Chinese, Laotians, Khmers, Mons. Some powerful Chinese merchants trading in the new capital were granted officials titles. After the king and his relatives, officials were powerful. They held numbers of phrai, commoners who were recruited as forces. Officials in Thonburi mainly dealt with military as well as 'business' affairs.
Despite Taksin's successes, by 1779 King Taksin was in trouble. He was recorded in the Rattanahosin's gazettes and missionaries's accounts as becoming maniac, insulting the senior Buddhist monks, proclaiming himself to be a sotapanna or divine figure. Foreign missionaries were also purged from times to times. His officials, mainly ethnic Chinese, were divided into factions, one of which still supported him but the other did not. Economic was also in turmoil. Famine attacked the kingdom. Corruption and abuses of the officials were rampant. The monarch attempted to restore order by harsh punishments. Numbers of officials and merchants, mostly ethnic Chinese, were reportedly executed. Discontent among officials was growing.
In 1782 Thonburi sent a huge army to subjugate nearby kingdoms such as Cambodia and Lao principalities again, but while they were away, a rebellion led by a powerful official broke out. The rebels eventually controlled the capital, forcing the king to step down. It is said that Taksin was allowed to be a monk. Later, the general, Phraya Chakri, the commander-in-chief of the army in Cambodia, who had wide popular support among officials, was offered the throne to King Taksin's commander in chief as he marched back from Cambodia and officially deposed king Taksin from monkhood. Taksin was secretly executed shortly after.