Japan attacked the US Pacific Fleet at its base at Pearl Harbor on 7 December 1941, but what led to that decision? Why did the Japanese attack the USA? - The answer is oil.

Japan had been modernising its economy throughout the 20th century and wanted to build an empire of its own. However, Japan lacked the natural resources to make it a reality, with all but 6% of its oil supply being imported. After capturing Manchuria, Japan became bogged down in a full-scale war with China in 1937 and had to look elsewhere for the resources it needed to fight. Meanwhile, the USA was slowly awakening from its isolationism.

When Japan occupied French Indochina in 1941, America retaliated by freezing all Japanese assets in the states, preventing Japan from purchasing oil. Having lost 94% of its oil supply and unwilling to submit to U.S demands, Japan planned to take the oil needed by force. However, striking south into British Malaya and the Dutch East Indies would almost certainly provoke an armed U.S response. To blunt that response, Japan decided to attack the U.S Pacific Fleet at Pearl Harbor, hoping that the U.S would negotiate peace.

The attack at Pearl Harbor was a huge gamble, but one which did not pay off. Though Japan took its objectives in the Pacific and Southeast Asia, the U.S did not respond as expected. Instead of reverting to isolationism, the U.S geared up for total war and Japan's fate was sealed.