After France surrendered to the Germans in the summer of 1940, Hitler allowed the resultant Vichy French government to maintain modest military forces, in order to defend Vichy France and the French colonies around the world. The Japanese, however, saw the situation in Indochina as an opportunity to pressure the local Vichy colonial government to cut off the flow of supplies into China, and to allow passage of Japanese troops. When the French hesitated to cooperate, the Japanese attacked French forts along the northern border of Indochina and bombed Haiphong harbor in September of 1940. After two days of heavy losses, Vichy officials agreed to the Japanese demands. These events made the Thais believe they had an opportunity to retake the ethnic Thai areas they had been forced to cede to the French decades before.
