Military history of Japan

The recorded military history of Japan began in 2nd century during the Yayoi period.

The Yamato tribal alliance fought amongst the Three Kingdoms of Korea, in the 5th century against Goguryeo and Silla and in 663 against Silla and Tang dynasty forces.

The Nara and Heian periods saw clan warfare and the subjugation of the Emishi people. The Kamakura shogunate began the Japanese feudal system, led by the shogun ruler, daimyo lords, and samurai warriors. The 15th to 16th century Sengoku period saw intense civil wars.

The 1603-1868 Tokugawa shogunate oversaw a relative peace. Its Satsuma Domain invaded and vassalized Ryukyu in 1609. The sakoku policy limited Japan from foreign influences, from 1641 until the 1853 United States Perry Expedition. The 1868–1869 Boshin War led to the Meiji Restoration and colonization of Hokkaido.

The Japanese colonial empire, inspired by Western imperialism, fought the First Sino-Japanese War resulting in the annexation of Taiwan in 1895. The 1904–1905 Russo-Japanese War establish Japan's sphere of influence over Manchuria and Korea, and Korea was annexed in 1910.

Japan invaded Manchuria in 1931, began the full-scale Second Sino-Japanese War in 1937, and invaded French Indochina in 1940. In 1941, Japan began the Pacific War, a major theater of World War II, against the Western Allies, occupying vast areas of southeast Asia including Malaya, the Dutch East Indies, and the Philippines. Japanese war crimes contributed to an Allied civilian death toll of over 26 million. Air raids on Japan killed over a million civilians in Japan. The US atomic bombings of Hiroshima and Nagasaki remain the only uses of nuclear weapons in warfare. Alongside the Soviet invasion of Manchuria, Japan surrendered in August 1945.

The US then occupied Japan until 1952, the only foreign occupation of Japan's history. Article 9 of the 1947 Constitution renounces war and the use of force in international disputes. The 1951 U.S.–Japan Alliance requires the US to defend Japan including extending its nuclear umbrella. In 2015, the Japanese government voted to reinterpret the constitution to allow collective self-defense of Japan's allies.

The Japan Self-Defense Forces, established in 1954, consist of the Japan Ground Self-Defense Force, Japan Maritime Self-Defense Force and Japan Air Self-Defense Force. The Prime Minister serves as commander-in-chief.