Why did Japan attack Pearl Harbor?Why did Japan attack Pearl Harbor?
The Japanese assumed that the United States would eventually enter the war, and they wanted to keep the pressure on the British during their occupation of Southeast Asia, particularly the Dutch East Indies. The Japanese hoped to destroy the entire American fleet which they discovered was stationed in Pearl Harbor, Hawaii. Their first-strike attack was aimed to permanently cripple the American naval fleet and leave the British without support in the Pacific theatre. The Japanese also hoped to buy more time to add to their own powerful naval fleet. Additionally, they hoped that the decisive attack would destroy American morale at home. In fact, it boosted American morale and united the country in their foray into the war. Luckily for the United States, none of their aircraft carriers were in Pearl Harbor at the time; and, though battleships seemed to be the main objective of the Japanese--they sank four U.S. battleships--during the remainder of the war, the aircraft carrier became the most dominant naval force. Pearl Harbor proved a crippling, but not deadly, blow to the American Navy, which swiftly rebuilt itself and later dominated the seas in both the Atlantic and Pacific theatres.
The biggest thing to understand here is that Japan was not trying to invade the Hawaiian Islands. Instead, it was trying to knock the US Pacific Fleet out of action so that Japan could take an empire in Asia withouth US interference.
Japan wanted an empire in Asia and felt that it deserved to have an empire just as the Western powers had empires. It needed an empire because Japan has very few resources -- very little iron or oil.
As Japan tried to take an empire, the United States expressed great disapproval, eventually ending trade with Japan after Japan took Vietnam in 1941. By ending trade with Japan, the US cut off Japan's supply of oil and iron.
Japan felt that it would be starved of those resources within two years, so it decided to go to war. It thought that a strike on Pearl Harbor was its only chance for success.
The hope of crippling American naval forces in the Pacific helped to motivate the Japanese Attack on Pearl Harbor. The belief was that the surprise and intense nature of the attack would permanently weaken the United States and help to catch the Americans by surprise. At the same time, there was a belief that the isolationist driven Americans would be susceptible to an attack, contributing to the overall motivation for the attack. Indeed, the surprise element was present. However, the Japanese ended up providing the ultimate rationale for going into war. It was not long after the attack that the United States ended up committing themselves in the conflict and both manpower and industrial might swayed towards the war effort which ultimately culminated in Japanese defeat.
We were the only remaining empire that was in Japan's way by 1941. They had conquered most of Asia, and the British and French were in no position to fight back, as they were either conquered by Germany already or fighting for their lives. Japan didn't want to fight us, they just figured their best chance was to knock out our navy so we could no longer threaten them.
A consensus had been reached from a series of imperial conferences that Japan would need to fight the US to obtain victory in Southeast Asia. To prevail in a protracted conflict, Japane needed high levels of raw materials and the only way to obtain the resources from Southeast Asia was to provoke the US into a war through a surprise attack. The attack on the US would give the Japanese the time they needed to attain the resources they required and to further expand its own industrial capability. It was thus necessary for the Japanese navy to first destroy the American Pacific fleet and challenge US naval supremacy since it was the only potent force that could halt the Japanese advance in the region. By destroying the battle fleets that were located at Pearl Harbour, Japan would be able to gain the time they needed to erect a giant barrier around Southeast Asia, which when guarded by the imperial navy, could keep the US at bay. A knockout blow at sea was also essential to gain the psychological ascendancy they needed to drag out the war so as to force the Americans out of it - they were sure that the Americans would not be invested into fighting a protracted conflict in a region that they would not familiar with.