Following a bloodless revolution in 1932, Siam became a constitutional monarchy and changed its official name to "Thailand".While it joined the Allies in World War I, Thailand was an Axis satellite in World War II.Various Indianised kingdoms such as the Mon, the Khmer Empire and Malay states ruled the region, competing with Thai states such as Ngoenyang, the Sukhothai Kingdom, Lan Na and the Ayutthaya Kingdom, which rivaled each other.European contact began in 1511 with a Portuguese diplomatic mission to Ayutthaya, one of the great powers in the region.
Its maritime boundaries include Vietnam in the Gulf of Thailand to the southeast, and Indonesia and India on the Andaman Sea to the southwest.
Although nominally a constitutional monarchy and parliamentary democracy, the most recent coup in 2014 established a de facto military dictatorship.
Tai peoples migrated from southwestern China to mainland Southeast Asia from the 11th century; the oldest known mention of their presence in the region by the exonym Siamese dates to the 12th century.
In the late 1950s, a military coup revived the monarchy's historically influential role in politics.
Thailand became a major ally of the United States and played a key anti-communist role in the region.