When Chiang forced the French to give the French concessions in Shanghai back to China in exchange for withdrawing from northern Indochina, he had no choice but to sign an agreement with France on 6 March 1946 in which Vietnam would be recognized as an autonomous state in the Indochinese Federation and the French Union. The agreement soon broke down.
On November 23, 1946, the French fleet began a naval bombardment of the Vietnamese sections of Haiphong that killed over 6,000 Vietnamese civilians in one afternoon. The Việt Minh quickly agreed to a cease-fire and left the cities. This is known as the Haiphong incident.
The bombardment of Haiphong by French forces at Hanoi only strengthened the belief that France had no intention of allowing an autonomous, independent state in Vietnam. The bombardment of Haiphong reportedly killed more than 6000 Vietnamese civilians. French forces marched into Hanoi, now the capital city of the Socialist Republic of Vietnam.