Currahee

Since the Japanese were not planning on invading the United States anytime soon, what was the reason behind attacking Pearl Harbor?

Was it just to show that they mean business?

Nemowork

They were being economically blockaded by the US so they couldnt get enough fuel and war materials to continue their war in China, keep the state running and expand their military and all the other things a young state trying to make a name for itself does.

they reckoned they needed to get out and secure those resources by invading the oil fields in the dutch territories.

they couldnt do that without setting off a war with the US who obviously didnt want Japan to get oil so they figured they could strike the US fleet, sink it and take over in asia quickly and the US would be so shocked at the loss of their fleet, unable to hit back because the Japanese would be militarily secure with their own intact fleet and a reliable fuel supply and so isolationist the US government would swallow their pride and come to a quick diplomatic solution.

It was a stupid idea.

diddyriddick

Pretty much spot on.

funakison

Very blinkered thinking by the Japanese

arras

It was to cripple US Pacific fleet at the beginning of war so it would be unable to interfere with Japanese early operations. I do not know any historical source which would suggest Japanese expected USA to capitulate as a consequence.

There is actually famous quote of Isoroku Yamamoto, man who masterminded Pearl Harbour attack saying that he can run wild first half of the year of war (in terms of military operations) but after that he can not guarantee anything. If that shows something than that Japanese command expected USA to fight back, Pearl Harbour or not.

Panthera tigris altaica

Yamamoto was one of those rare Japanese military officers. He spoke bluntly to his superiors and as a consequence his opinions were largely ignored by the rest of the military leadership.

arras

If you refer to fact that they proceed with war anyway than I do not think they had much other options. It was either war or surrender their empire and became de facto US protectorate. Yamamoto himself was not against war.

As of his opinions ignored I do not think that was the case. He was man who more or less masterminded, planed and led all early Japanese naval operations right until his death. It was his opinion which mattered more than anybody's else. Once decision to go to war was taken that is.

Panthera tigris altaica

They had an option open to them, Get out of China and abandon their empire. But that was not fully appreciated by Washington.

Let me rephrase that. His opinions on war and peace with the allied powers didn't matter to his superiors.

arras

Yes.

Well given surrendering empire was not really option for Japanese leading class, it was in a way irrelevant. But that did not necessarily had to be result of relations between Jamamoto and his superiors.

Also please note that Japan and USA were both preparing for conflict between each other more or less since end of WWII. It was obvious interests of these two countries gone clash at some point.

Poly

And on top of everything, the Japanese caused negligible damage to the US military at Pearl Harbor.

They got the worst of both worlds...an angered superpower and one that had barely suffered a scratch