USA spends very little money on military as a percentage of GDP while being the most powerful force in history. I would argue that that money is very well spent.

There is waste surely --but if we don't "police" then people complain the US isn't keeping the peace and they let dictators do as they wish. People want it both ways, they want the US to stabilize the world but they also want the US to keep out of other countries' business.

Trust me, nobody wants you to police the whole world. UN was formed for that very reason. US has over the years weakened UN to expand its own reach. So please get the hell out of everywhere and let UN handle.

UN is toothless without the US. Alas, US populace is tired of being chastised for spending massively and making mistakes on Pax Americana[0]. So, the US will increasingly isolate and won’t have the will to stand up to Russia and China aggression, which they are aware of and increasingly taking advantage of in the last decade. UK, France, and India aren’t formidable; not that they’d be willing. As you wish, we’ll find out how effective the UN’s deterrence is in the next decade.

[0] https://en.m.wikipedia.org/wiki/Pax_Americana

The UN is not much of a mechanism to rein in China or Russia anyway considering the structure of the Security Council.