The Allied Occupation of Japan began when Japanese representatives, aboard the American battleship Missouri, surrendered to the United States and its allies on September 2, 1945. Foreign Minister Shigemitsu Mamoru and Army Chief of Staff General Umezu Yoshijirō signed the surrender instrument by which Japan agreed to the Potsdam Agreement and surrendered its rights of sovereignty to the Supreme Commander for Allied Powers (SCAP), American General Douglas MacArthur, rights Japan did not regain until 1952.
As the occupation began, Japan's economic and social infrastructure lay in ruins. America's bombers and submarines had destroyed 43% of the buildings in 63 of Japan's 66 largest cities, 30% of all housing in the country, and 80% of Japan's ships. In 1945, rice production reached only 59% of the 1937 harvest, and Taiwan and Korea, major sources of imported rice, were no longer part of Japan's empire. Manufacturing had fallen to 53%, textile production to 6%, and processed food production to 32% of the prewar level. To add to the malaise, thirteen million demobilized soldiers, repatriated civilians from the lost empire, and unemployed workers from the disbanded weapons industry had to be housed and fed. In addition, rampant inflation caused by runaway wartime military spending undermined the value of the yen. General MacArthur and his staff and troops, never more than 150,000 after the first months of the occupation, took over a defeated nation in crisis.
Beginning in the fall of 1945, SCAP (a term which refers both to General MacArthur and to his headquarters) undertook three sets of programs: providing food, shelter and public health for millions of people in order to avoid famine and epidemic disease in the winter of 1945-1946, demilitarizing a polity dominated by the army and navy, and democratizing Japan.
Demilitarization included demobilizing Japan's soldiers and abolishing its army and navy, trying a large number of Japanese soldiers and civilians for specific wartime atrocities as well as a small number for their responsibility in planning and conducting the war, and in "purging" men identified as militarists from holding any kind of public office. To demobilize Japan's military, the allies forcibly brought over six million soldiers and civilians home from the former colonies and territories. One can imagine the burden this placed on allied shipping for a short period, and on the Japanese economy for a longer time. War criminals were divided into three categories for trial: over 4,000 Class C war criminals whom the allies tried for specific acts of brutality. Of these, the allies executed 700, sent 3,000 to prison, and acquitted the rest. Twenty Class B were tried because of atrocities carried out by soldiers under their command. Of these, the courts sentenced only two to death. Twenty-eight Class A war criminals, including the wartime Prime Minister, General Tōjō Hideki, were tried for crimes against humanity and for conspiring to fight aggressive war.
The trials for Class A criminals, which began in May 1946, did not end until November 1948, when seven of the defendants, including Generals Tōjō and Matsui Iwane, the Japanese commander in Nanjing at the time of the atrocities there in 1937-1938, were sentenced to death. Sixteen others received life sentences (all commuted within two or three years after the occupation's end) and two shorter sentences. The allies purged some 200,000 former "rightists" from public office-a ban that prohibited the purgees from serving as schoolteachers, village assemblymen, policemen, national railroad workers or in any other publicly funded position. Since the occupation authorities had no way of identifying which Japanese actually had been ultra-nationalists, they chose those to be purged by category. SCAP thus banned from public office all active military officers, all current mayors, even of the smallest villages (but not their predecessors), all school principals (but not assistant principals or ethics teachers), and all chiefs of village and town branches of the Imperial Military Reservist Association.