Japan, allied with Great Britain, took part in the First World War on the side of the Entente. By handing over the 21 demands of January 18, 1915 to the Chinese government, it tried to secure hegemony in China; Japanese troops occupied Shandong. 1918-22 Japan also occupied parts of Siberia. In the Versailles Treaty of 1919, the right to lease Kiautschou with Tsingtau, which had been conquered on November 7, 1914, was transferred to Japan; from the League of Nations the previously German Carolines, Marianas and Marshall Islands were assigned to him as a mandate for administration. In 1922, Japan joined the Washington Naval Agreement and took part in the Nine Power Pact to protect China and the rights acquired by foreigners there (1922), withdrawing from its 21 demands and clearing Shandong with Tsingtau.
Domestically, a two-party system had developed, which was based on the parties Seiyūkai and Kenseikai (since 1927 Minseitō) based. In 1922, the Communist Party of Japan was founded in illegality. According to militarynous, growth problems in industrial society and their effects (inflation, unemployment, etc.), which were expressed in unrest due to the high price policy for rice (1918) and in a general economic crisis (1920-22), not only pushed for socio-political solutions (e.g. welfare – and labor laws), but also constitutional (e.g. 1925 extension of the right to vote). Decisive for Japan’s further political development, however, was the increasing influence of radical nationalist officer groups in the 1920s, so that the change in electoral law only insignificantly strengthened the Reichstag. Politically decisive were the Secret State Council and the military senate founded in 1903 as an advisory body for the emperor.
On December 25, 1926, Emperor Hirohito (* 1901, † 1989) took office and put his reign under the guiding principle of »Shōwa« (Shining Peace).
Domestically, in the 1930s the turn to an ultra-nationalist policy caused momentous changes, some of which were caused by the plans to reorganize East Asia under Japanese rule. On February 20, 1928, elections to the Reichstag under universal suffrage took place for the first time; But just a few years later, especially after the Great Depression, which hit the export-dependent economy of Japan hard, the efforts of military-nationalist circles to eliminate the Reichstag and the “party cabinets” that had ruled since 1918 began to become more and more noticeable. As a result of a military coup in 1932 (“May 15 Affair”), Prime Minister Tsuyoshi Inukai, who was considered moderate, became Inukai murdered; In 1936 (“Affair of February 26”) a revolt of younger officers followed, which was suppressed on February 29.
In 1940 the chauvinist and anti-parliamentary groups were so strong that all political parties and movements, including v. a. those who were still trying to oppose the military had to disband. It was replaced by a kind of unity party, the Association in Support of Imperial Rule (Taisei yokusankai).
After an incident near Mukden (Shenyang) staged by Japanese officers on September 18, 1931, the conflict in Manchuria broke out: the three Manchurian provinces of China (Mukden, Jilin, Heilongjiang) and Jehol province were occupied by Japan by its Kwantung army; In 1932 the Japanese-dependent state of Manchukuo was constituted (on March 1, 1934, it became an empire under Pu Yi proclaimed). Since he was not recognized by the League of Nations, Japan declared its withdrawal from it (March 27, 1933). On November 25, 1936, the Anti-Comintern Pact was signed between Japan and Germany, which Italy joined on November 6, 1937. On July 7th, 1937 (fire exchange between Japanese and Chinese soldiers at the Marco Polo Bridge near Beijing) the Sino-Japanese War broke out. This was initially planned as a blitzkrieg, but then developed into an all-out war, the cruel leadership of which not only demanded high losses within the Chinese population (for example that after the conquest of Nanking [ Nanjing ] In December 1937 the Nanking massacre among the urban population, which claimed around 200,000–300,000 deaths), but also in Japan itself led to the material and spiritual mobilization of the whole country. With the declaration (1938) by Prime Minister Fumimaro Konoe (1937–39 and 1940–41) that an “East Asian sphere of prosperity” should be created in East Asia, Japan outlined its expansive foreign policy, which was aimed at conquering large parts of the Asia-Pacific region and thus was also directed against the interests and possessions of the Western powers (including the Japanese contracting parties Germany and Italy). The first steps on this path were the establishment (March 30, 1940) of a Chinese national government under Wang Jingwei (* 1883, † 1944) in Nanking (Nanjing) and further military advances towards Indochina. In response to Japanese action, the United States terminated the 1911 trade treaty in July 1939 and imposed economic sanctions, which Britain and the Netherlands joined. On September 27, 1940, the Tripartite Pact between Japan, Germany and Italy was signed. After Japan’s defeat in a military conflict with the USSR on the Manchurian-Mongolian border (1939), the two concluded a neutrality pact (April 13, 1941). With the attack on Pearl Harbor (December 7, 1941) and the declaration of war on the USA and Great Britain, Japan entered the Second World War, in which it was able to temporarily conquer all of Southeast Asia and the western Pacific region.
The major Japanese offensive, however, was stopped in April 1942 when the American air force attacked the main Japanese islands for the first time, and came to a complete standstill in the naval battle of Midway (June 1942) and in the fighting on Guadalcanal (until February 1943). After the Allied landings on Iwojima (February 1945) and Okinawa (April 1945), the war was lost for Japan. After the US dropped the atomic bombs on Hiroshima and Nagasaki (August 6 and August 9, 1945) and the Soviet declaration of war (August 8, 1945), Emperor Hirohito proclaimed The unconditional surrender of his country (after his personal decision of August 14, 1945) through a radio address on August 15, 1945 (on September 2, 1945, signing of the document of surrender on board the American battleship Missouri in Sagami Bay Tokyo).