While this definitely played a factor (I doubt the US would have had over 50% of the global GNP at the end of the war if their factories were getting bombed), t

While this definitely played a factor (I doubt the US would have had over 50% of the global GNP at the end of the war if their factories were getting bombed), the US was a global manufacturing powerhouse in 1937 by any measure; in both raw number of factories, and per-capita productivity the US was far ahead. The US had more manufacturing capacity than Germany and Japan combined before a single bomb was dropped on a German or Japanese factory.