I tend to take a Libertarian, Wilsonian view on the whole situation. We stay out of things until we're brought into them.
Remember the last time someone successfully mounted a large-scale attack on US soil? Remember what Roosevelt did?
Japan's surrender was practically immediate.
We should have gone in and reduced them to a nuclear wasteland, then had done with it. You hit me, I reduce you to rubble immediately and completely so that you learn your lesson, then we make up and you become such an economic power that you end up buying major sections of me.
Edit: Oh, fuzzbuckets. It was Truman that dropped the damn bomb. What with FDR having the stroke and all, I always get confused. Point still stands: Japan surrendered six days after the bomb was dropped. Now we do so much business with them that it borders on the ridiculous.