Japan underwent significant transformations under Emperor Hirohito's reign from 1926 to 1989.^[92] The early part of his rule saw the rise of extreme nationalism and expansionist military endeavors, including the invasion of Manchuria in 1931 and the Second Sino-Japanese War in 1937. The nation's aspirations culminated in World War II. Following its loss in World War II, Japan experienced foreign occupation for the first time in its history, before making a remarkable comeback as a leading global economic force.^[93]

In late 1941, Japan, led by Prime Minister Hideki Tojo, attacked the U.S. fleet at Pearl Harbor, pulling the United States into World War II and initiating a series of invasions across Asia. Japan initially saw a string of victories, but the tide began to turn after the Battle of Midway in 1942 and the Battle of Guadalcanal. Civilians in Japan suffered from rationing and repression, while American bombing raids devastated cities. The US dropped an atomic bomb over Hiroshima, killing over 70,000 people. This was the first nuclear attack in history. On 9 August Nagasaki was struck by a second atomic bomb, killing around 40,000 people. The surrender of Japan was communicated to the Allies on 14 August and broadcast by Emperor Hirohito on national radio the following day.

The Allied occupation of Japan from 1945–1952 aimed to transform the country politically and socially.^[94] Key reforms included the decentralization of power through breaking up zaibatsu conglomerates, land reform, and the promotion of labor unions, as well as the demilitarization and democratization of the government. The Japanese military was disbanded, war criminals were tried, and a new constitution was enacted in 1947 that emphasized civil liberties and labor rights while renouncing Japan's right to wage war (Article 9). Relations between the U.S. and Japan were officially normalized with the San Francisco Peace Treaty of 1951, and Japan regained full sovereignty in 1952, although the U.S. continued to administer some of the Ryukyu Islands, including Okinawa, under the US-Japan Security Treaty.

Shigeru Yoshida, who served as Japan's prime minister during the late 1940s and early 1950s, was instrumental in steering Japan through its post-war reconstruction.^[95] His Yoshida Doctrine emphasized a strong alliance with the United States and prioritized economic development over an active foreign policy.^[96] This strategy led to the formation of the Liberal Democratic Party (LDP) in 1955, which dominated Japanese politics for decades.^[97] To kickstart the economy, policies like an austerity program and the establishment of the Ministry of International Trade and Industry (MITI) were implemented. MITI played a critical role in promoting manufacturing and exports, and the Korean War provided an unexpected boost to the Japanese economy. Factors such as Western technology, strong U.S. ties, and lifetime employment contributed to rapid economic growth, making Japan the second-largest capitalist economy in the world by 1968.

In the international arena, Japan joined the United Nations in 1956 and gained further prestige by hosting the Olympic Games in Tokyo in 1964.^[98] The country maintained a close alliance with the U.S., but this relationship was often contentious domestically, as exemplified by the Anpo protests against the U.S.-Japan Security Treaty in 1960. Japan also navigated diplomatic relations with the Soviet Union and South Korea, despite territorial disputes, and switched its diplomatic recognition from Taiwan to the People’s Republic of China in 1972. The existence of the Japan Self-Defense Forces (JSDF), created in 1954, generated debate over its constitutionality, given Japan’s post-war pacifist stance as outlined in Article 9 of its constitution.

Culturally, the post-occupation period was a golden era for Japanese cinema, spurred by the abolition of government censorship and a large domestic audience. Additionally, Japan's first high-speed rail line, the Tokaido Shinkansen, was built in 1964, symbolizing both technological advancement and global influence. This period saw the Japanese population becoming affluent enough to afford a range of consumer goods, making the country a leading manufacturer of automobiles and electronics. Japan also experienced an economic bubble in the late 1980s, characterized by rapid growth in stock and real estate values.