International politics in modern times is a very complex subject. Just one century ago, at the time of the outbreak of the First World War, global politics looked much different. At that time vast empires ruled much of the world. The European powers drew political boundaries in manners that served the imperial will. Over the decades such empires collapsed almost without exception. As noted, the modern nation-state is viewed as the primarily legitimate form of governance, being related to the ideal of democracy. The power of these nation states is coordinated and exercised in some cases through transnational organizations – yet such transnational organizations are unlikely to replace the nation-state.
A state is simply a political entity. Government throughout the ages, from tiny island mayoralties to vast empires can be termed states. In this case the focus is on sovereign states, or those claim not to be bound by any external power. Most entities that are thought of as countries today can fall under this umbrella term of states. Nations on the other hand are groups referred that have a central and unique cultural as well as a historical identity. In modern times these usually overlap indicating the creation of nation-states.
In times past, the two were not necessarily synonymous. A vast empire could be called a single state, or government unit, but was comprised of many...