

It was a power grab. The US intervened softly to stop the growth of the third Reich into a hegemon, funding Britain, France, and the Soviet Union.
When Japan hit Pearl harbor Roosevelt was forced to war and honestly he and his team were probably itching to get in there are flex American power to shape events directly. Truman finished things out trying to box in the soviets once it was clear the allies were gonna win.



China has geographical problems that hamstring it against American Empire.
Until/unless they build a blue water navy that can blockade America or an alliance system that can shut us out of the indo-pacific, they are fucked in a straight up conflict.