I believe the world should be divided into twelve unions, containing four large states. These four large states will have the territory and resources to support a decent sized population, economy and military capability. This is important if those states want a confederation, instead of a federal relationship within the union.
I would support an eight-state union but for some reason there seems to be a weaker half. This half is normally politically divided as there isnt a strong culture to unite their geographical space. The junior half normally has a smaller population, economy and military capability.
There are exceptions to this such as Spain and Poland who have a strong united culture, but are still second to their other half France and Germany. The Euro Asian Union will be an exception in that it will need to become a federation, as Russia is the only unified culture.
There are four factors to determine if a union is required, territory, population, economy and military. This is not going to be a perfect science as a large territory may have lots of uninhabited areas. The populations in Asia greatly exceed other parts of the world. Military capability can be drastically different from one country to another, whether thats in quality or quantity.
Christopher E Packer