The Empire of Japan,[i] also referred to as the Japanese Empire, Imperial Japan, or simply Japan, was the Japanese nation-state[j] that existed from the Meiji Restoration in 1868 until the enactment of the reformed Constitution of Japan in 1947.[8] From 29 August 1910 until 2 September 1945, it administered the naichi (the Japanese archipelago and post-1943 Karafuto) and the gaichi (Korea, Taiwan, Kwantung Leased Territory, and pre-1943 Karafuto). The South Seas Mandate was a single Japanese dependent territory in the name of the League of Nations under Japanese administration. In the closing stages of World War II, with Japan defeated alongside the rest of the Axis, the formalized Japanese Instrument of Surrender was issued in compliance with the Potsdam Declaration of the victorious Allies, and Japanese de facto territory subsequently shrunk to cover only the Japanese archipelago as it is today.

Under the slogans of fukoku kyōhei[k] and shokusan kōgyō,[l] which followed the Boshin War and the restoration of power to the Emperor from the Shogun, Japan underwent a period of large-scale industrialization and militarization, often regarded as the fastest modernization of any country to date. All of these aspects contributed to Japan's emergence as a great power following the First Sino-Japanese War, the Boxer Rebellion, the Russo-Japanese War, and World War I. Economic and political turmoil in the 1920s, including the Great Depression, led to the rise of militarism, nationalism, statism and totalitarianism. This ideological shift eventually culminated in Japan joining the Axis alliance with Nazi Germany and Fascist Italy, and also conquering a large part of the Asia-Pacific.[15] During this period, the Japanese army committed many atrocities, including the Nanjing Massacre.