A return to independent city-states is probably the future of society. Unfortunately we're currently going in a direction of a one world wide government
I think a best case scenario would be popular-vote based local (metropolitan area) democracies, with a "world court" system that protects rights and arbitrates disputes between governments.
Another benefit of smaller independent city states is that it is easier to check their aggression. If raising a large army requires broad cooperation among city states, that greatly reduces the likelihood that such a force will come into being. This is because of the difficulty in coordination and the fact that multiple city states are unlikely to share the exact same interests, reducing their impetus to unite.