Europe is the third-most populous continent after Asia and Africa, with a population of 733 million or about 11% of the world's population. Europe, in particular Ancient Greece, is the birthplace of Western culture.[4] It played a predominant role in global affairs from the 15th century onwards, especially after the beginning of colonialism. Between the 16th and 20th centuries, European nations controlled at various times the Americas, most of Africa, Oceania, and large portions of Asia. Both World Wars were largely focused upon Europe, greatly contributing to a decline in Western Europeandominance in world affairs by the mid-20th century as the United States and Soviet Union took prominence.[5] During the Cold War, Europe was divided along the Iron Curtain between NATO in the west and the Warsaw Pact in the east. European integration led to the formation of the Council of Europeand the European Union in Western Europe, both of which have been expanding eastward since the fall of the Soviet Union in 1991.