It really depends on what you define a "World War" as. There have actually been more than two world wars in history because of how such conflicts as the Seven Years' War between England and France involved their colonies, including those in North America. The conflict that would have evolved without U. S. involvement after what we call World War I would have still included Eurasia, Africa, Australia, North America, and South America, all of the habitable continents. It would still have been a "World War".
I mean, given the situation that you've set out, you're talking about if World War II would have occurred after World War I. In that scenario, Hitler's Germany most likely would have continued his expansionist ambitions across Europe, Japan would have wished to become a major power in the Pacific, and Italy would have wanted to develop more African colonies. This would have run counter to interests in the U. S. as business would've sought resources from such places, and there would've been something of a push for war. Other factors would have contributed as well. Thus, I'd say that it was inevitable.