capital was occupied by the Burmese garrison army and five local leaders declared themselves overlords, including the lords of Sakwangburi, Phitsanulok, Pimai, Chanthaburi, and Nakhon Si Thammarat. Chao Tak, a capable military leader, proceeded to make himself a lord by right of conquest, beginning with the legendary sack of Chanthaburi. Based at Chanthaburi, Chao Tak raised troops and resources, and sent a fleet up the Chao Phraya to take the fort of Thonburi. In the same year, Chao Tak was able to retake Ayutthaya from the Burmese only seven months after the fall of the city. Chao Tak then crowned himself as Taksin and proclaimed Thonburi as temporary capital in the same year. He also quickly subdued the other warlords. His forces engaged in wars with Burma, Laos, and Cambodia, which successfully drove the Burmese out of Lan Na in 1775, captured Vientiane in 1778 and tried to install a pro-Thai king in Cambodia in the 1770s. In his final years there was a coup, caused supposedly by his "insanity", and eventually Taksin and his sons were executed by his longtime companion General Chao Phraya Chakri (the future Rama I). He was the first king of the ruling Chakri dynasty and founder of the Rattanakosin Kingdom on 6 April 1782. Modernisation and centralisation Under Rama I (1782–1809), Rattanakosin successfully defended against Burmese attacks and put an end to Burmese incursions. He also created suzerainty over large portions of Laos and Cambodia. In 1821, Briton John Crawfurd was sent to negotiate a new trade agreement with Siam – the first sign of an issue which was to dominate 19th century Siamese politics. Bangkok signed the Burney Treaty in 1826, after the British victory in the First Anglo-Burmese War. Anouvong of Vientiane, who mistakenly held the belief that Britain was about to launch an invasion of Bangkok, started the Lao rebellion in 1826 which was suppressed. Vientiane was destroyed and a large number of Lao people were relocated to Khorat Plateau as a result. Bangkok also waged several wars with Vietnam, where Siam successfully regained hegemony over Cambodia. From the late-19th century, Siam tried to rule the ethnic groups in the realm as colonies. In the reign of Mongkut (1851–1868), who recognised the potential threat Western powers posed to Siam, his court contacted the British government directly to defuse tensions. A British mission led by Sir John Bowring, Governor of Hong Kong,