Doing National Hari-Kari

World War II was a total disaster for Japan.  They suffered enormous casualties, we sank their navy, we sank their merchant marine, we nuked their cities, and the ones we didn't nuke, we firebombed.  Then we occupied the Home Islands, hauled Japanese leaders up in front of a War Crimes Trial, imposed a new constitution, and rewrote a lot of Japanese law to make it favorable to free market capitalism and democracy.  We ran the place until the 1950's. 
   A worse outcome to a war is hard to imagine. 
   And the leadership that took Japan to war with the United States knew they would loose. And they did it anyhow.  There was an independent staff study by top Japanese academics predicting total disaster.  There was Admiral Yamamoto who had spent a lot of time in the US, spoke English well, and he said "For the first six months we shall run wild, but I have absolutely no confidence after that."  There was Matsuota, the foreign minister who had grown up as a foster child in California.  The Japanese knew that America had a huge population, a vast national territory, highly industrialized, blessed with abundant natural resources, and out weighed and outclassed Japan in every category. They knew war with the US would lead to defeat.
   And, they should have known that they didn't need to go to war with the US.  Japan's national goal in those days was to take over China. They had made a good start, and there was no reason to beleive that they could not finish the job.  Japan was depending upon imports of iron and steel and crude oil from the Unitied States.  And we did not approve of a Japanese takeover of China.  We finally imposed an embargo (traditional American action) upon Japan.
    This put a bind upon the Japanese.  They all knew that they would run out of steel and oil in a matter of months.  But, there was plenty of oil in Dutch Indonesia, not far away.  Hitler had invaded and occupied Holland, which left the Dutch colonial regime in Indonesia kind of blowing in the wind.  Japan could have obtained plenty of oil from Indonesia, either by trade or by force.
   We, the Americans, would not have approved, but we had Nazi Germany to deal with.  The entire American establishment, political, military, business, the papers, all agreed that proper US strategy was to do Germany first.  Germany was bigger, stronger, more advanced, and closer than Japan. Plus the isolationists made life difficult for the Roosevelt administration to do anything internationally.   The Japanese should have known that they could do pretty much anything they wanted on their side of the Pacific, and all the Americans would do about it is write diplomatic nasty grams.  
   But, the Japanese plowed ahead and attacked Pearl Harbor.  They didn't have to do it, it led to a disastrous military defeat, they knew it would, but they did it anyhow.  

Conspiracy theories of History

One of them that's been going around since 1941, the Pearl Harbor disaster was caused by treason in the American government.  The government knew the Japanese air raid was coming a failed to warn the Pearl Harbor commanders.  Roosevelt's numerous enemies have accused him of conspiring to bring the US into WWII by setting up the Pacific fleet.
    I don't buy this.  Roosevelt wanted to intervene in WWII and was prevented from doing so by a powerful isolationist movement.  But, Roosevelt wanted to use the fleet to do the intervention.  The idea that he would sacrifice the fleet he looked to do the intervention, merely to silence domestic political opponents is absurd. 
   Pearl Harbor happened because US commanders thought Pearl was so far away from Japan as to be immune to Japanese action.  They just could not imagine getting hit at Pearl.  Even though the Royal Navy had pulled off a very similar air strike on the Italians at Taranto just a few months before. 
   Pearl even ignored a radar warning.  The US Army had a working radar station on Hawaii.  It picked up the incoming  Japanese strike 180 miles out.  The Army radar operators telephoned a warning to fleet headquarters but the junior officer of the day ignored it.  If  fleet HQ had had it's act together, this was enough warning to scramble aircraft and call for battle stations, get the guns manned and the ammunition broken out of locked storage. 
   Pacific Fleet also ignored a report from a picket destroyer that had detected, depth charged, and sunk a submarine lurking right off Pearl, in a restricted zone,  where no submarines had any business being.  To ignore both a submarine warning and a radar warning the same morning takes a remarkable degree of stupidity.