Determining whether certain territories are states or not is at times difficult. Some places are universally not seen as sovereign states. To one country a territory maybe seen as a state, but to another it isn't. It's based off perspective in some aspect, but for the most part more than enough countries recognize the same territories as states. 

     A nation state is a state that contains a single nation. There are very few nation states in the world. A perfect example is Iceland, and somewhat Japan. With nation-states, these states are all unified under one common nationality, they learn the same material, so on and so forth. One state rules over that single nation. This differs because, even though a person would rule over their territory, many different cultures, and nationalities were there. It is difficult to have nation-states still present becase of how diverse many countries tend to be. It differs from earlier ways because in the past people wouldn't consider themselves part of a nation. They stayed where they were, and didn't need that label, but would probably identify by their region or local lord.