Nah, I don't think that's accurate at all. FDR's entire strategy was to save capitalism. That was also the Nazi's goals. The problem was that the Soviets were winning, and that for Nazi Germany to win they would take over the European economy and America would have to take junior partner status. If Nazi Germany both didn't need all of Europe and also could actually beat the Soviets, the US wouldn't have been involved at all.

Japan had no capability to invade the USA and could not extend its empire to the USA. It attacked Pearl Harbor to get the USA out of the Pacific so it could have China, Korea, SE Asia all to itself. America could have responded to that without doing anything with Korea and without intervening in the Chinese civil war. Instead the US nuked Japan to demonstrate to the Soviets that they would destroy them if they tried to take the rest of Europe, then took Korea over from Japan to stop the Soviets from spreading into the peninsula, and then intervened in the Chinese civil war to protect the nationalist KMT and create the Taiwan situation.

The idea that the US had no horse in the race is contradicted directly by all the available evidence.