Well, I'm fairly sure the US was aware of the German atomic programme.
IIRC that was started later than the US one. Anyways it had hardly gotten very far by the time the war was over.
Al - of course it's still "more likely" ... it's also more likely that I will strangle you if we ever meet than if we never meet, but that alone is no reason not to ever meet anybody.
A situation as in Somalia is the kind of problem I was thinking of when I said it throws up a no. of problems, though... or just the fact that countries are, in essence, artificial entities whose borders can change at very short notice.