I'm not saying what Japan did was in any way noble, but it was certainly far from unexpected. The US administration knew the war in Europe was a serious problem if left unchecked, that Britain and its allies would never prevail, but there was considerable resistance to the war.
The attack on Pearl Harbor instantly catalyzed support.
This doesn't even touch on the fact that many American companies were looking at Germany as an important customer, a country spending lavishly to build up its capability, at a time when American companies were struggling.
Politics are complicated. It's rare that any of those involved in a conflict are entirely innocent.
