The theory behind the US having a large military is that it acts as a sort of fleet in being - that the US prefers other methods of engaging with countries, and having a stronger military precludes other countries from engaging militarily. In turn, having stable global relations and protected global trade provides the US with a huge economic boon to fund its large military.

That's the theory anyway - our Idiot King and his idiots have completely missed the point of the US military existing and are using it as a primary method of engagement, which is causing the economic boon used to fund the military to evaporate.

As an aside, it's not a huge issue, but China's military costs use different accounting than the US, and seem lower by comparison. Apples to apples, China probably spends about half what the US does on military.