International alliance refers to arrangements between state parties that bind them to cooperate in military, diplomatic and economic ways in support of a common cause. Such a cause can be national security or a variety of other goals. A key characteristic of an international alliance is that the member states are willing to relinquish some of their sovereignty to achieve a shared purpose. This can create tensions because some states have to sacrifice more of their sovereignty than others, leading to dissatisfaction and frustration. Also, the extent to which a common goal is achieved varies considerably among members.
The idea of an international alliance has long been linked to the concept of spheres of influence and the balance of power. The modern concept of the international system, however, has led to a greater emphasis on cooperation among states in peacetime. As a result, many scholars and policymakers have reevaluated the role of alliances in the international system.
Some observers have argued that the formation of international alliances requires an external threat, and that a lack of one leaves no reason for them to continue. Other scholars have emphasized the importance of social, cultural and political similarities and of alliances as tools for constraining state behavior.
NATO, for instance, was reformed after the Cold War to expand its mission beyond a defense-oriented focus on European borders and to confront threats that are outside of its territory. NATO members are committed to a defense budget of 5 percent of their GDPs, and the alliance has a range of military capabilities at its disposal.