The Attack on Pearl Harbor: Why the US Entered WWII
A Japanese carrier force attacked the US naval base at Pearl Harbor, O'ahu, Hawaii, on 7 December 1941 and so brought the United States into the Second World War (1939-45). The surprise attack, made before war was officially declared, caused over 3,500 casualties and destroyed or seriously damaged 18 ships, including eight battleships. Crucially, the US aircraft carriers were not in Hawaii at the time, and vital supply dumps and repair facilities were left intact. As a consequence, the US Navy was eventually able to recover. Japan, having taken over most of Southeast Asia in 1942, was gradually pinned back during the Pacific War to hold only its own islands. Japan surrendered in August 1945 following the dropping of two atomic bombs. The US had gained the ultimate revenge.
The Japanese Empire
By late 1941, Japan's military government had already occupied Manchuria, Formosa (Taiwan), Korea, parts of coastal China, and the north of French Indo-China (which included what is today Laos, Cambodia, and parts of Thailand). A setback to Japanese expansion came in the summer of 1939 when its forces were defeated by those of the USSR in the border region between Manchuria and Outer Mongolia. The Japanese army suffered 18,000 casualties at the Battle of Nomunhan (aka Khalkhin Gol). This defeat gave the Japanese navy one more argument in its favour that the Pacific should be Japan's next area of conquest.
The expansion of Japan's military required massive quantities of raw materials which Japan simply did not have. Nor could the Japanese buy these resources. A US embargo on oil, gasoline, iron ore, coal, copper, steel, lead, tin, rubber, and nickel was imposed in order to induce Japan to withdraw from China and protect US interests in places like the Philippines. British Malaya and the Dutch East Indies (Indonesia) also restricted oil sales to Japan. Japanese financial assets in US banks were frozen, severely limiting Japan's ability to buy oil. By mid-1941, Japan felt obliged to acquire the resources it needed through conquest.
In April 1941, a Soviet-Japanese non-aggression pact was signed, which permitted Japan to concentrate on its growing empire to the south. In July 1941, Japan attacked southern Indo-China. On 1 December 1941, the Japanese government decided it would declare war on the United States, Britain, and the Netherlands. The Japanese military government felt that, sooner or later, these states would declare war on Japan anyway if it continued its expansion in the Pacific, particularly if it attacked the oil-rich areas of British Malaya and the Dutch East Indies. An attack on the US's allies Britain and the Netherlands would surely provoke the US into finally entering the war.
A preemptive strike on the US Navy, it was hoped, would allow Japan to dominate this theatre of WWII. The destruction of as many US ships as possible would be essential since the Japanese Navy could not compete with the numerically larger US Navy and the much more powerful economy of the US in the long term. An attack plan had been devised by Admiral Yamamoto Isoroku (1884-1943), Commander-in-Chief of the Combined Fleet. A large aircraft carrier group would sail secretly to Pearl Harbor in Hawaii, home of the US Pacific Fleet. Japanese planes would then use newly developed torpedoes to sink US aircraft carriers and battleships while they were still in port.
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⇒ The Attack on Pearl Harbor: Why the US Entered WWII
