Well, what fused it was Japanese nationalism.
The embargo left them with only a humiliating option.
The preparations, or rather lack of them, was a high-up command screw-up.
(The Brits already used that kind of attack on the Italian fleet, as well as that the U.S. already had radar sets on Hawai, - from the Brits I belive)
The radar and command events that sad morning were U.S. local screw up.
So, it was screwed. To make it worse, the thing was repeated to the USAAF under McArthur's command in the Phillippenes several hours later, and by that time the high command already knew of the hostilities. Still, them B17's were knocked out on the ground while standing parked tip-to-tip.