That's out there. It is a combination of our very effective embargo and that we knew they were coming but needed the Pacific Fleet destroyed so we could declare war on Germany.
And yes, the embargo was damn effective, maybe the most effective of any embargo. Japan was desperate for oil. All that is true. We never had a clue they were coming. The Japanese changed their code just before leaving, they also changed their call signs. The radio operators of a couple of ships were transferred to island stations and sent fake signals, knowing that we could tell it was the usual Akagi radio operator sending it. It was all very elaborate, and we had very little chance to break it in a month.
The Japanese attack on Pearl Harbor achieved as nearly complete a surprise on an opponent as any in military history. Ever since the first bombs fell
www.historynet.com
And we were mired in old thinking, Billy Mitchell wasn't yet a hero. We firmly refused to believe that carriers were the new ultimate naval weapon.
Oh, and we only declared war on Germany after Germany declared war on us. America wasn't wanting revenge on Hitler, I'm not sure we would have declared on Germany without the German gambit.