The Nguyễn dynasty remained the formal emperors of Annam and Tonkin within Indochina until World War II. Japan had occupied Indochina with French collaboration in 1940, but as the war seemed increasingly lost, overthrew the French administration in March 1945 and proclaimed independence for its constituent countries. The Empire of Vietnam under Emperor Bảo Đại was a nominally independent Japanese puppet state during the last months of the war. It ended with Bảo Đại's abdication following the surrender of Japan and August Revolution by the anti-colonial Việt Minh in the August 1945. This ended the 143-year rule of the Nguyễn dynasty. Many Vietnamese historians have a harsh and poor assessment of the Nguyễn dynasty.