For the sake of my argument, let us assume that any association of people (along any lines) which can (and do) kill another group of people is a State. We are not talking about murders between individuals. But groups of people attacking other groups of people in general and sometimes indiscriminately in wars.
From such simple assumptions, we can create an entire branch of study about States in general without imposing any ideology.
- There may be other associations between people of a State which are religious, economic, class-based, caste based, trade based, tribal, familial, racial and ideological. However, any association among these that can kill/attack people in wars forms the State.
- As you have seen above any form of association can become a State as soon as it can start to designate other groups of people as enemies to be killed in groups/indiscriminately.
- A World State will not have another group of people to kill because it wants to be a State of all people. The only way it can kill groups of people is if it starts declaring that some people are not human enough for whatever reason. Declaring people as non-human has often lead to atrocities unimaginable.
- To prevent such a possibility, the World State will have to give up its ability to kill people, and thus not become a State, while simultaneously, removing the ability of other States it consolidates, to kill.
- In such a World State, over time other harmless associations (like religions/tribes/races) will become capable and willing to define, attack and kill its enemies. However since the World State has given up its ability to define and kill enemies, it will be not able to protect against this new 2nd State. And thus we cease to have one world government.
Thus, under our definition of the State, either a World State will cease to be State over time or it will declare people as non-human and conduct unimaginable crimes against them.