It is commonly thought that the 20th century witnessed two world wars. It would be more accurate to say that the century had but one world war, with a 21-year intermission. More specifically, a case can be made that World War II was a result of American intervention in the First World War.
Counterfactual history is a risky endeavor.
The Great War began in August 1914. America did not enter the war until April 1917. By that time both sides were exhausted from years of grinding warfare. There is ample reason to believe that had nothing new been added to the equation, the belligerents would have agreed to a negotiated settlement. No victors, no vindictiveness.