How would the war have ended if America had not intervened? The carnage might have continued for another year or two until citizens in the warring nations, who were already protesting the endless sacrifices required, forced their leaders to reach a settlement.
Or the war could have dragged out another decade, bankrupted all the major European nations, and caused the rise of communism/fascism in even more countries. Or maybe everyone in Europe would still be fighting each other rather than arguing over trade rights and interest rates. It's dumb to talk about what might have happened differently with any degree of certainty, and a professor of history should probably know better.
Personally, I'm not a fan of this style of essay anyway. It's disingenuous to act like you're just presenting the facts of history, and that all of the facts just so happen to align with your own viewpoint. There's probably a good discussion to be had over whether or not it was worth sacrificing the lives of American citizens in a European war, whether the shady things the Germans were doing justified a US military response, whether economic justifications for entering a war are ever acceptable, or whether war can ever improve a situation, but there isn't any of that here.