You've been watching too much Star Trek.
I am fully aware that what I describe cannot just be done, but it does not mean it's not the right thing to strive towards. Even the countries we have now have been split up into smaller, warring tribes if you go back far enough. It's always been the resistance, the hardships that have forced us to cooperate, and it mostly still is. Climate activism is a good example, there's a common enemy, "clearly" defined rules of what is right and wrong, it gets people together, even across nationality and religion. But while there are lots of proof that people can cooperate against a common enemy, there's no proof they can't cooperate without one, oftentimes it seems most resistance to that idea is people refusing to believe that others can do it, and then the suggested change itself becomes the common enemy, and prevents it from happening.. There may be some what to make people agree, it's just not been found yet.