Costa Rica can start this off. They are demilitarized already. The Maldives can start this off. Any nation or people can start. We start with a simple pledge. It is a plausible path to fight climate change. It is a plausible path to make significant economic change.
The pledge says: Our nation will demilitarize if every other nation does so as well. That is, every nation must make the pledge before it comes into force. That will just be the beginning of dialogue and planning. But nothing happens until the US, Russia, and China make the pledge. Countries can maintain minimal defense forces. A scaled back and unified international force, like the UN, can also exist.
As these pledges are made, diplomacy becomes easier. Many border disputes become easy settlements.
We can look to religions, usually beacons of peace, to guide the way. They can encourage their followers to take the pledge.
Nations across Latin America, Africa, the Pacific, and any other nation that can benefit from a united world can make the pledge. If 100s of nations have pledged, it will push others.
There would be a presidential campaign in the US running on a UBI. That is because we have an extraordinarily large military budget. We can allocate a large portion of that to UBI. Combine that with a revved up global economy on top of global cooperation and global unity.
This is a winning strategy for radical economic change. This is a winning strategy for climate change.
The so called global south can demand change from the global north.