Provinces ceded to Thailand by France 1941; Wikimedia Commons
From 1940-1941, Vichy France and Thailand fought to control certain areas of French Indochina that had once belonged to Thailand. On May 9, with Japanese mediation, a peace treaty was signed in Tokyo that forced Vichy France to relinquish disputed border territories.
Although ostensibly a Thai victory, Imperial Japan was able to expand their influence in both Thailand and Indochina.