International relations, relationships between nations, through politics, treaties, military confrontation or cooperation, economics, or culture. Peacetime contact is generally maintained through diplomacy; each nation maintains embassies in other countries it recognizes as nations. Even when states do not maintain mutual embassies, however, they may find it desirable to keep contacts open, often through the offices of a third nation. The other primary link is through membership in various international organizations, either for global politics (e.g., United Nations), defense (NATO), or simply mutual convenience (Universal Postal Union). From 1946 on international relations were dominated by the concept of the Cold War, in which the complications of world diplomacy were reduced to an oversimplified model of an ideological contest between 2 global antagonists, the communist and capitalist systems as personified by the Soviet Union and the United States. In the 1960s the rise of the Third World countries negated this simple division, though many of these countries took one or the other side. In the 1970s relations between the United States and the Soviet Union improved, largely through trade and nuclear limitation agreements and also because of the rise of China as a rival superpower. The endurance and value of the resulting detente, however, remained doubtful as the 1980s saw new—and continuing—areas of conflict between the superpowers. In 1990, the Charter of Paris for a New Europe was signed by the United States and the Soviet Union, effectively ending the Cold War.