Various science fiction writers (perhaps most notably, Mack Reynolds) developed the theme that multinational coporations with their own armed forces would displace the nation state as having a "legal monopoly" on the use and threat of violence to impose ordere. The stories were interesting, but to me, unconvincing.

The nation-state has only been the biggest player on the political field for about 500 years; earlier we find alternative arrangements, whether empires, feudal estates or city states.

For what it is worth, my guess is that something along the lines of a city-state may displace the nation-state as a focus of power--combined with some sort of (am not clear in my mind on this at all) world order to suppress pirates and terrorists.

Rarely do I venture on predictions, but here is one: The twenty-first century is going to be as different from the twentieth as the twentieth century was from the seventeenth century. In other words, I think we live in a time of major discontinuity. I suspect that different regions of the world will have extremely different outcomes over the next hundred years. Or to put it differently, I think the "prophets of globalization" who predicted a convergence of living standards and lifestyles throughout the world were and are 100% wrong.