There is a technological bend to making the world smaller, that is for sure. We can communicate worldwide instantly. This makes us forget about our human nature. We are predisposed to small groups. It is how our brains work. This is why large empires inevitably crumble. People resent being controlled by strangers. Look at the English empire and the USSR for recent examples of crumpling empires.
I foresee a future filled with small city-states something akin to ancient Greece. All of our decentralizing technology can aid each small community prosper and compete.
I truly think the competitive interplay of a thousand city-states would enhance our world much more than some monolithic uber world state ever could. Think of it, not happy with recent legislation or high taxes in your town? Pack up and move to a neighboring city were freedoms are greater with a lower tax burden. Governments would have to be competitive to keep its citizens, not arbitrarily handing down heavy handed edicts from some uber state like the EU where you have no say in the matters of taxation or immigration.
Those are some good points, especially about people wanting to stay in smaller groups. I guess with decentralising technology, we can stay in smaller groups while being a part of a much larger one. So, that way, a one world state would only be for name sake.