You know, maybe like 10-20 years ago there would have been no doubt that standalone, the US is strongest. But now the US is deep in debt from all their wars, the dollar is cheap, and the economy is not tip top. If there was a real war, you'd have to take in account allies, and strategy. Ally-wise, the US doesn't really have any, a lot of countries hate america and the others are just kinda neutral. Strategy-wise, I'd guess it depends on how smart the people working for both sides are.