Lets say we decide to pull out of world affairs and become isolationist just like we were prior to WWII. no more Nato, no more bases or soldiers etc.. We decide not to care if the Russians march into the Ukraine etc. If Countries in Europe etc.. were forced to build up their own militaries would they still be able to provide the same social benefits/early retirement they offer today? I would imagine things would drastically change if they had to spend a ton of money to protect themselves on their own dime. No more massive social services for the people?
I think a better question would be would China make a better Defense provider than the United States.