Following the Fall of France in 1940 , Major-General Plaek Pibulsonggram ( popularly known as `` Phibun '' ) , the prime minister of Thailand , decided Deciding that France 's defeat Conquering gave Giving the Thais an even better chance to regain Getting the vassal state Statement territories that were ceded Surrendering to France during King Chulalongkorn 's reign .

This seemingly subservient behaviour convinced Convincing the Phibun regime that France would not seriously resist Defending a confrontation with Thailand .