Japanese invasion of French Indochina
Following the Fall of France in 1940, Thais perceived a chance to regain the territories they had lost years earlier. The collapse of Metropolitan France made the French hold on Indochina tenuous. After the Japanese invasion of French Indochina in September 1940, the French were forced to allow the Japanese to set up military bases. This seemingly subservient behavior convinced the Thai regime that Vichy France would not seriously resist a confrontation with Thailand.