FDR was desperately trying to find a way into the European and Pacific wars well before Pearl Harbour. By then, for example, he'd taken over the protection of Atlantic convoys for half of their journey to Britain. He'd also introduced peacetime conscription for the first time in US history, and started a huge military build up - again a first in peacetime, since until then the US had generally maintained rather anemic land forces except during war. The Republicans were hardline isolationists, and with a minority of the Dems made a declaration of war politically impossible.

I'm also not sure how the chaotic mess that was China in the thirties posed any sort of competition. Russia for its part was an ally of Germany's until it got attacked.

And, bluntly, what could we have done about it anyway?  Particularly in Europe the heads of the governments really didn't pay a lot of attention to what we had to say, and we didn't have many more divisions than the pope.  France was still reeling from the loss of a generation, Germany surging with national pride wanted a place in the sun (colonies), Italy with its meglomaniac and the English still looking down their noses at the wogs.  None of them in power were likely to listen to us, they had doom to meet.

I've always thought that the absolute horror and folly of that war is what strengthened the European populations to get control of their governments to make sure that this didn't happen again and knocked the virulent forms of nationalism out of their political structures for 2 generations as a respectable public expression.

"I said, 'Wait a minute, Chester, You know I'm a peaceful man...'" Robbie Robertson