In December 1941, the US joined the Allies in war against the Empire of Japan, a monarchy. After the Allied victory, Japan was occupied by Allied forces under the command of American general Douglas MacArthur. In 1946, the Japanese Diet ratified a new Constitution of Japan that followed closely a 'model copy' prepared by MacArthur's command, and was promulgated as an amendment to the old Prussian-style Meiji Constitution. The constitution renounced aggressive war and was accompanied by liberalization of many areas of Japanese life. While liberalizing life for most Japanese, the Allies tried many Japanese war criminals and executed some, while granting amnesty to the family of Emperor Hirohito. The occupation was ended by the Treaty of San Francisco.