All will agree that it is safe to say theories are not always practical and clear cut. Theories can only be perfected and carried out as they are intended to be in hypothetical world. With that being said, I will answer to the question of whether the world should be organized into sovereign territorial nation-states. Should it? Under the assumption that theories can be applied to the world with no exceptions, it is indeed ideal for the world to be organized into politico-military rule of nation-states, not only because it is the final and best form of politico-military rule having been invented so far, but also in order to have a sense of organization and order in the Global society, and to efficiently communicate with one another, and to cause the least possible conflict and clash among the entities that exist in the world.
Like Opello and Rosow mention in their book, The Nation-State and Global Order, there are three alternatives of nation-state: city-state, empire, and tribe. There should be various reasons why rule of nation-state is the most efficient form and best fit of all for the world of the present age. To mention one of them, nation-state is the most effective in dealing with physical territorial issues among the world. City-state is incapable of expanding its size because of its incapacity and inefficiency of governing bigger area. Empire and tribe mostly don’t have a sense of territoriality, since they don’t usually have defined territory of their jurisdiction. In the world complex and complicated like today’s world, they are not the most efficient forms of entities theoretically and practically, especially when it comes to dealing with physical territorial issues among entities.
Order and system are very crucial in civilizations and, even in ‘uncivilized’ the world of nature, there exist some type or form of order and system. There is no civilization without order and system and there always is civilization where order and system exist. As the humanity becomes more ‘civilized,’ and to become even more so, it requires of order and system or some sort. I think it is legitimate to say that civilization is mostly establishing order, system, or rules in society. In the same sense, it is critical that there should be a rule or standard agreed by all to keep things in order and to make the world politics work nicely with no confusion. Since the nation-state is the most sufficient and developed politico-military rule so far, it is, at all, agreeable that it should be the basic rule or qualification to have a voice in world politics. By recognizing one another as nation-states, which implies that they also recognize all of the characteristics of nation-state, there established are system and order that make the world coexist effectively. By making those groups on the same social or political level, as nation-states with the same kind of rights and authorities, it makes communication among them become much easier and effective communication brings less conflict amongst those parties.
In reality, however, there can be exceptions and situations in which this does not apply nicely. To name one of the examples, ethnical and cultural conflict can occur within a nation-state or between nation-states that were unconsciously established by stronger countries of the time without considering the nation-state’s tendency to be homogeneous (i.e. the case of some of African countries) In those cases, a sense of unity and national identity, which is one of the characteristics of nation-state, has failed and so it needs to alter or be flexible to fix the problem. In some cases or possible exceptions that could exist in the practical world, the rule of being organized into nation-states can be modified and fitted according to different cases.
Theoretically and ideally, the world should be organized into territorial sovereign nation-states by every mean. However it might require some modification or flexibility on some of the practical issues that can be faced in World Politics.