There is a say that variety is the spice of life, so if human in their own wisdom is trying to create a system where we're going to have
i.One Government
ii.One currency and
iii.One religion
Which I have heard most people talked about , I think that is the beginning of the end,
Because trying to unify the whole world and financial system will be destruction at the end.
You can create a single state and a single people, but at the same time give people the opportunity to show their individuality.
In the future, people will be able to create their own experimental states (country), but these states will have a certain limited duration of their existence. It will be possible to create an experimental state (country) with a certain social system - capitalism, socialism, communism, a monarchy, a republic, etc. Such temporary states will be created for scientific purposes. They will allow you to test certain scientific hypotheses.
People will also be able to freely change their citizenship. Today I can declare myself an elf (citizen of Gondolin), and tomorrow a goblin or a hobbit, and the day after tomorrow I will come up with something of my own.
But all this can be done within the framework of one nation and state.