ALLIANCE

in international relations, a formal agreement between two or more nations for mutual support in case of war. An alliance provides for combined action on the part of two or more independent states and is usually defensive in form, since it obligates allies to join forces if one or more of them is attacked by another nation. Alliances are typically defined by a treaty, the most critical clauses of which are those that define the casus foederis, or the circumstances under which an ally becomes obligated to aid a fellow ally. Alliances arise from nations' attempts to maintain a balance of power with each other. In a system composed of a number of medium-sized states, such as that in Europe since the Middle Ages, no one state has been able by itself to establish any lasting hegemony over all the others, largely because the other states would join together in alliances against it. Thus, Louis XIV's repeated attempts to achieve continental dominance provoked the formation of a Grand Alliance against France, and Napoleon's ambitions were similarly thwarted by a series of coalitions formed against him. Ideology need not play the deciding role in such coalitions. In 1536, for example, Francis I, the Roman Catholic king of France, joined with the Ottoman sultan Sleyman I, who was a Muslim, against the Holy Roman emperor Charles V, another Catholic, because Charles's possessions almost encircled France. A new stage in the alliance-building process in Europe began in the late 19th century, when enmity between Germany and France polarized Europe into two rival alliances. By 1910 most of the principal nations of Europe belonged to these great opposing alliances: Germany and Austria-Hungary formed the core of one bloc (the Central Powers), while France, Russia, and Great Britain formed the other (the Allies). This bipolar system had a destabilizing effect, since conflict between any two members of opposing blocs carried the threat of general war. In the event, conflict between Russia and Austria-Hungary in 1914 quickly drew their fellow bloc members into the general conflict known as World War I (191418). The war's outcome was effectively decided when the United States abandoned its traditional isolationism and joined the Allies in 1917. The Allied victors in the war sought to ensure the postwar peace settlement by forming the League of Nations. The league operated by a collective security agreementi.e., one calling for joint action by all of the league's members to defend any individual member or members against an aggressor. A collective security agreement differs from an alliance in several ways: (1) it is more inclusive in its membership; (2) the target of the agreement is unnamed and can be any potential aggressor, including even one of the signatories; and (3) the object of the agreement is to deter the aggressor by the prospect that preponderant power will be organized and brought to bear against him. The League of Nations became ineffective in the mid-1930s, however, after its members declined to use force to stop aggressive acts by Japan, Italy, and Germany. These three nations soon formed the Axis, an offensive alliance that contested for world dominion in World War II (193945) with a defensive alliance led by Great Britain, the Soviet Union, the United States, France, and China. With the defeat of the Axis powers in 1945, the victorious Allies formed the United Nations (UN), a worldwide organization devoted to the principles of collective security and international cooperation. The UN coexisted rather ineffectively, however, with the robust military alliances formed by the United States and the Soviet Union along sharp ideological lines after the war. In 1949 the United States (and Canada) joined with Britain and other western European countries to form the North Atlantic Treaty Organization (NATO), while in 1955 the Soviet Union and its central and eastern European satellites formed the Warsaw Pact. The global rivalry between these two alliances, known as the Cold War, only ended with the Soviet Union's collapse in 1991. Alliances in modern times have required a joint effort far more integrated than was called for by alliances in earlier times. Thus, for example, in the coalitions of World War II, combined agencies for military and economic planning were a common and conspicuous feature. Even in less tightly knit alliances, such as NATO, great importance has been attached to close and cooperative action, both military and political, particularly in the context of the 20th-century strategy of nuclear deterrence.