What Benefit for the Average US Citizen Comes from being the World's Policeman?

Dan Carlin had a thought provoking podcast about what benefit do Americans gain from our country being the world policeman. We spend 20% our tax monies on our military and "policing" the world. We spend almost as much money on our military as the entire rest of the world. It costs us dearly, but the average American does not benefit from all that money. Would that we would spend some of that money on curing cancer, ending migraines, or finding a cure for Alzheimer's.