1935, Mar 2 - King Rama VII abdicates, leaving no successor. The National Assembly proclaims his nephew, Prince Ananda Mahidol, a boy of 10, as legal heir to the throne. As the proclaimed monarch (who is given the title of Rama VIII) is underage and aside of that staying with his family in Switzerland where he attends school, the National Assembly appoints a Council of Regency to act on his behalf.
1938, Dec 16 - Pridi Panomyong, aided by the army group of Phibul Songkhran, a key military leader in the suppression of the attempted coup d’etat of 1933, oust Prime Minister Bahol from his post. Phibul Songkhran is appointed prime minister by the Council of Regency. He concurrently takes the post of Minister of Defense. Pridi Panomyong becomes Minister of the Interior.
1939 - A drift toward military dictatorship begins. The prime minister’s assumption of complete power negates the idea of constitutional and democratic government.
1939, Sep 3 - World War II begins in Europe and Siam declares neutrality. To be protected from outside aggression, Siam signs a treaty with Japan making Siam an ally of the Japanese who in exchange recognize her territorial integrity.
1940, Jun 12 - Non-aggression pacts are also concluded by Siam with Britain and France.
1941, Dec 7 - Siam and Japan clash as Japan demands free passage through Siam to attack the English territories and Thais resist.
1941, Dec 8 - Japan starts the war in Asia and the Pacific by bombing Pearl Harbor, Hawaii, the Philippines and Singapore. While Winston Churchill advises Siam to defend herself, Siam allows free passage to Japanese troops. Japan promises to respect Siam’s independence and sovereignty.
1941, Dec 21 - Japan and Siam sign an alliance pact which includes the agreement that Tokyo will help Bangkok get back territories lost to Britain decades earlier. Siam in return undertakes to assist Japan in the war against the US and the United Kingdom.
1942, Jan 25 - British and American planes begin raiding Bangkok and Siam declares war on the UK and the US.
1942 - Phibul Songkhran comes into complete control of the government without any organized opposition. He concentrates on foreign affairs and international politics, hoping to bring power to Siam.
1942, Dec 1 - Communist forces that have been operating in Siam since 1927 formally organize the Communist Party of Siam.
1943 - Pridi Panomyong organizes an underground resistance movement against the Japanese in Siam, in cooperation with the Free Thai Movement in the US, founded by the Siamese Ambassador to Washington, Seni Pramoj who had earlier refused to deliver Prime Minister Phibul Songkhran’s declaration of war against the US to the US government. This action helps Siam gain the sympathy and support of the allies.
1944, Jul - Phibul Songkhran’s government is toppled by its own National Assembly.
1944, Aug - Khuang Aphaiwong (1902 - 1968), still a member of the original group of the People’s Party that staged the revolution against the absolute monarchy, is appointed the new prime minister. He returns to titles of nobility as well as the old system of writing and drawing, all of which had been abolished by Phibul Songkhran whose main intention, aside from personal power, had been to turn Thailand into a more modern country. All political prisoners are released.
1945, Aug 15 - Word War II ends.
1945, Aug 16 - With approval of the National Assembly, Siam’s declaration of war on the US and Great Britain is repudiated by Pridi Panomyong, at that time the sole Regent of Siam in behalf of King Ananda Mahidol who still studies in Switzerland.
1945, Sep 1 - Prime Minister Khuang resigns from office and the disobedient former ambassador to Washington, Seni Pramoj, becomes new prime minister. Khuang organizes the Democratic Party, the first political party in Siam composed of conservative and monarchist groups.
