People tend to think that Pearl Harbor was a "sneak attack" by imperialistic Japan and the US justifiably fought evil Japan. But President Roosevelt knew it and let Japan attack first so that the US could join the war in Europe and beat Japan which was trying to counter Western invasion into Asia (remember most countries around the world were colonized by the West back then. In Asia, only Korea, Japan and Thailand were left uncolonized. Even parts of China were taken by Britain, France, Germany, Russia, etc).
McCollum memo on 1940.10.07 to Roosevelt (one year before Pearl Harbor) indicated 8 actions to corner Japan, including complete trade embargo with Japan, and concluded, "If by these means Japan could be led to commit an overt act of war, so much the better. At all events we must be fully prepared to accept the threat of war".
America (A), British (B), China (C), Dutch (D), or ABCD encirclement closed Straight of Malacca, and stopped minerals and oil from being shipped to Japan. In addition, the US imposed complete ban on oil, despite desperate diplomatic efforts by Japan. Japan imported oil mostly from the US, and with the ban, only 2 years reserve was left. This was a matter of life or death for Japan - waiting meant losing the nation without fighting. Having realized these facts, General MacArthur testified in the US Senate later in 1951, "They (Japan) feared that if those supplies were cut off, there would be 10-12 million people unoccupied in Japan. Their purpose, therefore, in going to war was largely dictated by security".
Henry Stimson, then US secretary of State, in his diary stated that the issue was "how we should maneuver them (Japanese) into the position of firing the first shot without allowing too much danger to ourselves".
People tend to think that Japan went into the war for the purpose of invading Asia, in the spirit of imperialism and expansionism, but this is naive. They need to think what kind of world it was back then, and why Japan decided to go into the war against the US, a super power that had 80 times more resources than Japan did.
Read more in the Pearl Harbor Deception
http://www.apfn.org/apfn/pearl_harbor.htm
See BBC documentary "Sacrifice at Pearl Harbor"
https://www.youtube.com/watch?v=7p1TOA99S88
