Japanese invasion of French Indochina
The German military occupation of Metropolitan France rendered France's hold on its overseas possessions, including French Indochina, tenuous. The colonial administration was now cut off from outside help and outside supplies. After the Japanese invasion of French Indochina in September 1940, the French were forced to allow Japan to set up military bases. This seemingly subservient behavior lulled the Phibun regime into believing that France would not seriously resist a military confrontation with Thailand.