ABSTRACT
The nation-state was not born overnight, precisely at the moment the Treaty of Westphalia was signed, but was the product of a gradual historical process. This chapter presents international relations history into three periods: the international system in the seventeenth, eighteenth, and nineteenth centuries; the international system in the twentieth century; and the contemporary international system. One development was the emergence of only two states as the dominant actors in the international system—the United States and the Soviet Union. The second related development was the emergence of a highly polarized system in terms of alignment patterns, that is the East-West axis of conflict waged between two cohesive blocs organized around rival ideologies and led by the two superpowers. Between 1945 and 1975, the number of nation-state actors more than doubled from roughly 60 to more than 130, completely altering the world map.
