In June 1932, a group of foreign educated students and military men called “The Promoters” (คณะราษฎร) carried out a bloodless revolution, seizing power and demanded King Prajadhipok, granted the people of Siam a constitution.
The King inevitably agreed and in December 1932 the people were granted a constitution, ending 150 years of absolute Chakri rule. From then on the role of the monarch was relegated to that of a symbolic head of state. His powers from then on were exercised by a prime minister and the national assembly.