The causes of the attack on Pearl Harbor stemmed from intensifying Japanese-American rivalry in the Pacific. Japan’s imperial ambitions had been evident from as early as 1931, when she invaded Manchuria. The conquered region’s bountiful resources were then used to supply Japan’s war machine. Leaving the League of Nations in 1933, Japan pursued an aggressive foreign policy aimed at creating the ‘Greater East Asia Co-prosperity Sphere’, a euphemism for a Japanese empire modelled on European ones of the 19th century.
Japan became seen as a serious threat to the economic interests and influence of the US and European powers in Asia. By July 1937, with Japan engaged in all-out war with China, relations plunged to new lows. US President Roosevelt imposed economic sanctions, and Japan turned to the Axis powers, signing the Tripartite Pact with Germany and Italy in September 1940.
When Japan occupied French Indochina in July 1941, Roosevelt continued to avoid direct confrontation. But Japan’s imperial ambitions in the Pacific had placed her on a collision course with the United States, which controlled the Philippines and had extensive economic interests throughout the region. When the US imposed an oil embargo on Japan, threatening to suffocate her economy, Japan’s response was to risk everything on a massive pre-emptive strike which would knock the US out of the Pacific, clearing the way for a Japanese conquest of resource-rich South East Asia.
The Japanese achieved complete surprise at Pearl Harbor, something that can largely be attributed to failures in US intelligence. Although the US had cracked Japanese radio codes, in this case the raw data was not interpreted correctly by army and navy. Although the attack pummelled American battleships, US aircraft carriers escaped unscathed. This was critical because the Pacific Fleet would have been virtually incapable of operating without them.
The following day, the US declared war against Japan, where a shared sense of outrage and hatred had united the country’s bitterly divided media and public behind Roosevelt. On 11 December 1941, Germany and Italy declared war on the United States, thus bringing America into World War II.
Pearl Harbor appeared to be a huge success for Japan. It was followed by rapid Japanese conquests in Hong Kong, Singapore, Burma, the Philippines, Malaya and New Guinea. Yet in the long term, the attack was strategically catastrophic. The ‘sleeping giant’ had been awoken, and in America, a sense of fury now accompanied the mobilisation for war of the world’s most powerful economy. The losses at Pearl Habor would soon be more than made good, and used to take a terrible vengeance on Japan.