Invading Siamese forces attempt to exploit the political chaos in Vietnam, but are ambushed and annihilated at the Mekong river by the Tây Sơn in the Battle of Rạch Gầm-Xoài Mút.
The Battle of Rch Gm-Xoi Mt (Vietnamese: Trn Rch Gm Xoi Mt, Thai: -) was fought between the Vietnamese Ty Sn forces and an army of Siam in present-day Tin Giang Province on January 20, 1785. It is considered one of the greatest victories in Vietnamese history.
The Rattanakosin Kingdom (Thai: อาณาจักรรัตนโกสินทร์, pronounced [ʔāːnāːt͡ɕàk ráttāná(ʔ)kōːsǐn] (listen), or shortened to, รัตนโกสินทร์, Thai pronunciation: [ráttāná(ʔ)kōːsǐn]) is the fourth and present Thai kingdom in the history of Thailand, which was formerly known as Siam until 1939, and briefly in 1946. It was founded in 1782 with the establishment of Rattanakosin (Bangkok), which replaced the city of Thonburi as the capital of Siam. This article covers the period until the Siamese revolution of 1932.
The maximum zone of influence of Rattanakosin included the vassal states of Cambodia, Laos, Shan States, and the northern Malay states. The kingdom was founded by Rama I of the Chakri Dynasty. The first half of this period was characterized by the consolidation of the kingdom's power and was punctuated by periodic conflicts with Burma, Vietnam and Laos. The second period was one of engagements with the colonial powers of Britain and France in which Siam remained the only Southeast Asian state to maintain its independence.Internally the kingdom developed into a modern centralized nation state with borders defined by interactions with Western powers. Economic and social progress was made, marked by an increase in foreign trade, the abolition of slavery and the expansion of formal education to the emerging middle class. However, the failure to implement substantial political reforms culminated in the 1932 revolution and the abandonment of absolute monarchy in favor of a constitutional monarchy.