Siamese revolution of 1932

The Khana Ratsadon staged a coup d'état in Siam on 24 June 1932. It ended Siam's centuries-long absolute monarchy rule under the Chakri dynasty and resulted in a bloodless transition of Siam into a constitutional monarchy, the introduction of democracy and the first constitution, and the creation of the National Assembly.

Source: Wikipedia — Siamese revolution of 1932 (CC BY-SA 4.0)