On July 20th, 1948, the Siamese constituent assembly voted to change the name of siam to thailand, to change to come into On July 20th, 1948, the Siamese constituent assembly voted to change the name of Siam to Thailand, the change to come into effect the following year. Muang Thai or Thailand means ‘land of the free’ and the name had been changed before, in 1939 under the fascist military dictatorship of Field Marshal Luang Phibunsongkhram, but the anti-Axis powers refused to recognise the new name after Siam allied herself with the Japanese and in 1942 declared war on the United States and the United Kingdom.