[dgoldstein0]

well sure not everyone needs a huge military. Especially when their large trading partner has one and is guaranteeing security.

I don't entirely buy your personalities argument - it certainly mattered, but in an alternate universe where Hitler still rose to power but e.g. FDR didn't get a 3rd term - a European war would've still caused problems for America and US/Europe trade would've likely come under fire dragging the US towards fighting in the war; in 1939 US GDP was $93.4 billion with $3.2 billion in exports and $2.3 billion in imports... far less important than today (where imports/exports are more than 10% of GDP) but still fairly substantial.

But it's hard to say how things would've turned out. With different leaders the politics of it would've mattered a lot; without US support WWII could've still easily been raging in 1944, an election year, and so an anti-war president could've been replaced. Or maybe Britain would've had a hard time holding out against constant assault without American supplies purchased with US government money, the USSR wouldn't have been able to bear the full brunt of Nazis who were less tied up on the western front, and by the time America considered joining the war under a different leader, it would've looked like a go-it-alone job. Still it's hard to imagine a world in which the Axis didn't bite off a bit more than it could chew.