An agreement between two or more states to work together on mutual security issues. States enter into such cooperative security arrange- ments in order to protect themselves against a common (or perceived) threat. By pooling their resources and acting in concert, the alliance partners believe that they can improve their overall power position within the international system and their security relative to states outside the alliance.

Alliances can be either formal or informal arrangements. A formal alliance is publicly recognised through the signing of a treaty in which the signatories promise to consider an attack on any one of them as equivalent to an attack on all of them. The North Atlantic Treaty Organisation (NATO) is a good example of a formal security alliance. Informal alliances are much looser and less stable and rely, to a large extent, on the word of the parties involved and ongoing cooperation between them. The latter may entail, among other things, joint military exercises, the sharing of strategic information, or promises of assistance during a military crisis. Informal alliances can also take the form of secret agreements between leaders.

There are a number of benefits in forming alliances. First, they can offset the cost of defence. It is much cheaper for a state to ally itself with a stronger state that possesses a nuclear capability than it is for that state to build and maintain its own infrastructure, technological expert- ise, and weapons delivery systems. This makes alliances especially attractive to small, vulnerable states. Second, alliances can provide increased economic benefits through increased trade, aid, and loans between alliance partners. The deployment of foreign military personnel can also be beneficial to a local economy.

From the point of view of the great powers, alliances can provide them with a strategic advantage with respect to their actual or potential enemies. The United States, for example, entered into a number of bilateral alliances after 1945 in order to gain landing rights, access to ports, and the use of military facilities in strategically important loca- tions around the periphery of the former Soviet Union. Alliances can thereby help to contain an enemy and control a region of strategic interest. In addition, alliances can be useful in maintaining hegemonic control over one’s allies, encouraging them to ‘bandwagon’ with the great power as opposed to ‘balancing’ against it!

The lifespan of alliances varies. Some last for many years. This may have to do with a long-lasting perception of threat, similarity of polit- ical systems between member states, or the existence of a powerful hegemon. Other alliances decay fairly quickly. The so-called ‘Grand Alliance’ between Britain, the former Soviet Union, and the United States during the Second World War is a good example. It lasted only as long as Hitler remained a threat to world peace. As soon as Germany was defeated in 1945, the alliance broke down. Also, a state may bow out of an alliance if it no longer feels that its partners can fulfil the terms of the alliance.

Finally, leadership and ideological changes among member states may undermine an alliance.

Liberal internationalists from Immanuel Kant onwards have argued that alliances are a source of conflict between states. After the end of the First World War, US President Woodrow Wilson suggested that alliances drew states into webs of intrigue and rivalry. On the other hand, realists tend to argue that states form alliances based on their national interests. A change in the national interest can and should prompt states to rethink the terms of their alliance membership. Alliances should be regarded as highly flexible arrangements that can play an important role in maintaining the balance of power.

It is important to note that alliances are not simply beneficial secur- ity arrangements for ‘peace-loving’ states. They can be used to pro- mote aggression as well. The alliance between Germany, Italy, and Japan during the Second World War is a good example. Moreover, alliances may themselves be provocative instruments of foreign policy. It may well be the case, for example, that an alliance between two states is regarded as a hostile act by a third state. Under these circumstances, an alliance may lead to an arms race. It is for this reason that some states (such as Sweden and Switzerland) have traditionally pursued a policy of neutrality and non-alignment in Europe.

See also: balance of power; cold war; collective security; common secur- ity; concert of powers; national interest; North Atlantic Treaty Organisation; realism; security dilemma

Further reading: Reiter, 1996; Snyder, 1997; Walt, 1997