This is a question to have each nation take care of itself for it’s defense and peace.
For a model, every nation could have it’s own militia which should be large enough to handle any internal insurgency, like in Afghanistan with the Taliban. They should be equipped and be able to muster any more troops as needed. They should assume the charge of managing their own internal and external defense with democracy, peace and properity the rules of the day.
The militia could also be used for relief in natural disasters and need only be the size generally accepted as appropriate to their region though similarly capable given their recent history and without outside intervention e.g. U.S. troops could stay home from anywhere with a good independent militia.
Pass it on if you like it. It is mostly about peace and properity and security for it.
Thank you.
Sover N1