It's less a question of American economic power and more a question of the tens of thousands of American troops stationed throughout Europe. The U.S. military presence already in Europe is larger than the militaries of many European countries, and there's almost a million more American troops who can be deployed there if need be. If the U.S. was willing to do that in 1918, instead of turning isolationist again, World War II could have been prevented, just as the Pax Americana after World War II successfully prevented World War III.