Alliance

The term “alliance” is widely used, but it is often applied loosely and imprecisely.

For Glenn Synder, “[a]lliances […] are formal associations of states for the use (or non-use) of military force, intended for either the security or the aggrandizement of their members, against specific other states, whether or not these others are explicitly identified. The restriction to military means and security purposes excludes, obviously, such things as voting blocs in international organizations, customs unions, or collaboration on environmental problems. The restriction to states rules out transnational associations of all kinds, including especially ties between governments and revolutionary groups in other states. The proviso "specific other states" calls attention to the need for an adversary and differentiates alliances from organizations, such as the League of Nations or the United Nations, which are designed to provide collective security against any aggressor, including members of the organization itself” (Snyder 1990).

Stephen Walt defines an alliance more broadly as “a formal or informal relationship of security cooperation between two or more sovereign states. This definition assumes some level of commitment and an exchange of benefits for both parties; severing the relationship or failing to honor the agreement would presumably cost something, even if it were compensated in other ways” (Walt 1987).

He deliberately chooses not to make a formal treaty a necessary condition, because many states prefer not to enter into a formal treaty while nonetheless engaging in a de facto alliance. For example, there is no mutual defense treaty between the United States and Israel, but in practice it is clear that they are close partners who provide each other with security assistance.

Across the board, the term alliance is reserved to agreements that include an obligation to mutual military assistance in case of an attack by a third party. Present-day examples of such alliances include the North Atlantic Treaty Organization (NATO) or the Treaty of Mutual Cooperation and Security between the United States and Japan.