[dgoldstein0]

perhaps the US would be mostly safe from violence, but not consequences. We're heavily dependent on international trade and any major war in another part of the world will impact us if it involves any important trading partners or their ability to trade with us.

Even in the 19th century the US was sucked into Europe's wars - the war of 1812 was essentially the American theater of the Napoleanic war - US merchants were attacked trying to trade with France/Europe, the US Navy tried to protect them saying "we're neutral let us trade" and Britain said "there's no such thing as neutral" and sent armies. Over time foreign powers got more wary of fighting the US but we still got dragged into European and Pacific wars (WWI, WWII), in large part because we kept trading with our European and Asian partners.

[vkou]

Nearly everyone in the world is heavily dependant on international trade.

They all manage to get by without the leverage of 11 carrier fleet groups. You know, trade between equals, and not subjects.

WW2 was largely driven by the personalities involved. Roosevelt really, really, really hated fascism, and was doing everything in his power to stick it in their wheel spokes. Had the industrialist coup succeeded, or had Hoover or Landon won, it's quite likely that neither would have done much to oppose either Japan or Germany.

WW1 was also driven by principles, as opposed to pragmatism. Wilson found more alignment with the anglosphere than he did with the central powers - and after watching the most destructive war in history go on for four years, was keen on embarking on his League of Nations project. Practically, there was no reason for the US to not maintain neutrality in it.

[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.