If you review history, large wars broke out between the major powers vying for dominance on a regular basis in the 19th and early 20th century, culminating in the First and Second World Wars. For all the negatives of what the US has done with its military since then, they're not a hundredth as bad as what went on before by any objective measure.
The Pax Americana has been good for stability and with stability comes prosperity. If the United States truly gave up its hegemony and turned isolationist, you'd see a resurgence of rearmament and jockeying for power among nations, inevitably followed by a new era of war after war.