Policeman and MP control trafic at the intersection of Ginza 4chome, 1946 (Showa 21). From "Tsukon no Showa. Graphic Report"

Japan accepted the terms of the Potsdam Declaration on 15 August 1945 (Showa 20), that ended Pacific War.Japan then was placed under the occupation of the Allied Powers, led by the United States. Thereafter, the General Headquarters, Supreme Commander for the Allied Powers (GHQ/SCAP) issued directives to the Japanese Government, implementing various reforms based on the major policies of demilitarization and democratization.

With Japan's defeat in the war, the political parties, which had suspended party activities during the war, reemerged, and they resumed their active rolls. The Japan Socialist Party, the Japan Liberal Party, the Japan Progressive Party, and the Japan Cooperative Party were formed one after the others, and the Japan Communist Party was legalized. Japan's initial postwar election held in April 1946 (Showa 21), saw women exercise their franchise for the first time. Thirty Nine were elected as well as many other freshmen Diet members. The Japan Liberal Party emerged as the leading party.

The SHIDEHARA Cabinet had pursued the task of constitutional reform right after the war, but, the eventual Government proposal for a new Constitution followed the outlines of the draft drawn up by GHQ. The Diet then conducted its deliberations based on it. The new Constitution of Japan was promulgated on 3 November 1946 (Showa 21), resting on the principles of popular sovereignty and pacifism. At the sametime, directives from GHQ led to other wide ranging political and economic reforms, such as the purge of "undesirables" from public office, land reform, and the dissolution of the zaibatsu. The Japan Socialist Party became the ruling party in the general election of April 1947 (Showa 22), and its leader, KATAYAMA Tetsu, assumed the post of Prime Minister in a three party coalition Cabinet.

The opening ceremony of the Japan Peace Treaty Conference, held in the San Francisco Opera House, September 4, 1951 (Showa 26) From "Yoshida Naikaku"

The labor movement in Japan became quite powerful as a result of the occupation's democratization policies. The intensification of the Cold War between the United States and the Soviet Union, however, saw a shift of Occupation policies, including the end of the purge on "undesirables" from public office, and an increasing crackdown on leftists. General Douglas MACARTHUR directed Prime Minister YOSHIDA Shigeru to establish a National Police Reserve after the outbreak of the Korean War in June 1950 (Showa 25). In September 1951, the San Francisco Peace Treaty was concluded, along with the U.S.-Japan Security Treaty. Japan's place in the international community as an independent nation was restored in April 1952 following the treaty's ratification.