We became a superpower when Theodore Roosevelt sent our ships halfway around the world and swiped Spain's colonies. That's why our participation in WW1 was critical to bringing that conflict to a swifter resolution.
If FDR had been more interested in something other than spreading communism, WW 2 would have been unnecessary IMO.
As a result of FDR's Lend-Lease, we supplied our allies with what it took to win WWII, with our suffering way fewer casualties than our allies did, and we became the wealthiest nation in the world with everyone else being in debt to us. FDR deserves the credit for that.