Japanese invasion of French Indochina
In September 1940 a group of Japanese officers, in spite of an agreement signed the 22nd, attacked Đồng Đăng and laid siege to Lam Sơn, beginning the Japanese invasion of French Indochina. In March 1945 the Japanese again attacked, and it was the site of the fiercest fighting of the March coup d'état, when a company of Tonkinese Rifles and a battery of colonial artillery held off the invaders for three days before being massacred by them.