In 1937, Japan invaded other parts of China, precipitating the Second Sino-Japanese War (1937?1945), after which the United States placed an oil embargo on Japan. On December 7, 1941, Japan attacked the United States naval base in Pearl Harbor and declared war on the United States and the United Kingdom. On December 8, Netherlands declared war on Japan. This act brought the United States into World War II. After the atomic bombings of Hiroshima and Nagasaki in 1945, along with the Soviet Union joining the war against it, Japan agreed to an unconditional surrender of all Japanese forces on August 15 (Victory over Japan Day).

The war cost Japan and countries part of the Greater East Asia Co-Prosperity Sphere millions of lives and left much of the country's industry and infrastructure destroyed. The Allied powers repatriated millions of ethnic Japanese from colonies throughout Asia.[36] The International Military Tribunal for the Far East, was convened by the Allies (on May 3, 1946) to prosecute some Japanese leaders for war crimes. However, all members of the bacteriological research units and members of the imperial family involved in the conduct of the war were exonerated from criminal prosecutions by the Supreme Commander of the Allied Forces.

In 1947, Japan adopted a new pacifist constitution emphasizing liberal democratic practices. The Allied occupation ended by the Treaty of San Francisco in 1952 and Japan was granted membership in the United Nations in 1956. Japan later achieved spectacular growth to become the second largest economy in the world, with an annual growth rate averaging 10% for four decades. This ended in the mid-1990s when Japan suffered a major recession. Positive growth in the early twenty-first century has signaled a gradual recovery.[38]

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