I don't consider Einstein an American (he did all his stuff while living in Europe), and the bomb would have been invented with or without him.
Yup, that crossed my mind too, and even more so with regard to Enrico Fermi.
...and the bomb would have been invented with or without him.
OMG! Yes, you're right of course, except that its invention would be in our future rather than in our past. :)