That's in some ways how the EU is working out, although the global state is smaller and the city states are more like regions. The EU provides a single market,

That's in some ways how the EU is working out, although the global state is smaller and the city states are more like regions. The EU provides a single market, a customs area, freedom of movement and to some degree a currency. Most of the former Communist states are a lot smaller than 19th century imperatives would have dictated. In the EU and EU accession countries, there's Poland (40m), Romania (20m), and then all other countries are 11 million and below. And in Western Europe the independence movements are about spin-offs of similar populations. Scotland is 5 million, Catalonia is about 7.5 million (5 million in Barcelona), Brittany is about 4.5 million, the Italian city states a bit smaller. That's the way things are going.