Thailand does not have an independence day, since it did not fight for its independence from another country; however, as of 2014, the country celebrated December 5 as its national day. Thailand celebrates the king's birthday as its national day, so until a new heir ascends to the throne, the country will celebrate the day on King Phumiphon's birthday.
The country officially became Thailand on June 23, 1939. Before then, it was known as Siam. It was renamed after the major ethnic group in the country, although the name was switched back and forth again before officially returning to "Thailand" again in 1949.