Siam Declares War on Germany and Austria-Hungary
In 1917 Siam declared war on Germany, mainly to gain favour with the British and the French.
Siam's token participation in World War I secured it a seat at the Versailles Peace Conference, and Foreign Minister Devawongse used this opportunity to argue for the repeal of the 19th century treaties and the restoration of full Siamese sovereignty. The United States obliged in 1920, while France and Britain delayed until 1925. This victory gained the king some popularity, but it was soon undercut by discontent over other issues, such as his extravagance, which became more noticeable when a sharp postwar recession hit Siam in 1919. There was also the fact that the king had no son; he obviously preferred the company of men to women (a matter which of itself did not much concern Siamese opinion, but which did undermine the stability of the monarchy because of the absence of heirs).
Thus when Rama VI died suddenly in 1925, aged only 44, the monarchy was already in a weakened state. He was succeeded by his younger brother Prajadhipok.
Vajiravudh, an absolute monarch, he ruled and reigned from 1910 until 1925. He was one of the sons of King Chulalongkorn, the modernizing Siamese monarch introduced to non-Thai specialists in Rogers and Hammerstein’s The King and I.