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In the technical language of statesmen and scholars the term “alliance” signifies a promise of mutual military assistance between two or more sovereign states. Although some propagandistic advantages may be gained by applying the term to loose agreements for cooperation, such as the United States program for Latin America known as the Alliance for Progress, this use obscures the peculiarly far-reaching commitment contained in military pacts by which a nation formally promises to join another in fighting a common enemy.

Alliances are instruments of national security. They are sought in order to supplement national armed forces. The military support that is promised will usually, but not always, comprise the dispatch of military forces in time of need. It is not necessarily limited to such assistance. One country may also give the other permission to deploy forces on its territory or the right to move forces across its territory. Alliances may extend to forms of cooperation other than military ones, but they are unlikely to survive if the military reason disappears. When a country promises military assistance without receiving a similar promise in return, it is customary to speak of a guarantee pact. The guarantor may enter into such a pact when an enemy take-over of another, usually weak country would strike a blow at the guarantor’s security.

To be an effective instrument of security, the treaty must define as clearly as possible the circumstances known as casus foederis, under which the promise of mutual assistance is to become effective. Prior to World War I, alliance treaties usually contained a nonprovocation clause by which an ally was relieved of its obligations if its partner became guilty of provoking the war in which assistance was expected. The clause came into disrepute because it made it easier for a country to evade its obligation on the ground that its ally had caused the war. Remembering the lack of a firm British commitment prior to the war of 1914, the French have insistently claimed that military pacts lack deterrent value if the promised assistance is not virtually automatic.

No alliance is likely to be an unqualified blessing: in some cases it may prove more of a drain on a country’s strength than a supplement, and uncertainty is inherent in any promise of future assistance. The outstanding asset of an alliance is the military assistance expected in case of need and its deterrent effect on the enemy, even preceding any armed conflict. Moreover, a country may gain prestige from having powerful allies or from denying them to its opponent. The chief liability of an alliance is the obligation to come to the assistance of an ally possibly under conditions that, from a strictly national point of view, might suggest abstention from the conflict. A country fearing that the cost of involvement or “entanglement” in the quarrels of others will not be compensated by gains from the alliance may decide to “go it alone.” The weak country often fears that it may become dependent on an ally who can involve it in wars it can do nothing to prevent; the strong one fears that it will lose its freedom of action by tying itself to another.

Development. Despite these inhibitions, wherever in recorded history a system of multiple sovereignty has existed, some of the sovereign units when involved in conflicts with others have entered into alliances. Changing alliance patterns characterized interstate relations in ancient China from the eighth century b.c. to the middle of the third century a.d.; alliances were an accepted technique of foreign policy in ancient India, as shown by Kautilya in his Arthaśāstra (c. 300 b.c.). The polarization of the world of Greek city-states has been described by Thucydides in the Peloponnesian War, and the pitfalls of alignment and neutrality in the days of the Italian city-states have been examined by Machiavelli. Only within a system dominated by a single country, such as the Roman Empire, has there been little room for alliances.

Alliance policy became a specially prominent feature of the Western state system with the rise of nation-states in the fifteenth century. Coalitions of allied states were repeatedly formed against countries assumed to be seeking hegemony, and they, in turn, led to the formation of rival coalitions, as in the case of the Triple Alliance and the Triple Entente that preceded World War I. The establishment of the League of Nations did not dissuade France—a long-time advocate of alliance policy—from seeking security through a network of alliances during the interwar period. These alliances proved too weak, however, to deter Nazi Germany. Following World War II, the renewal of alliance policy came to center in Washington. Under the threat of Soviet expansion the United States broke with its traditional policy of nonalignment or isolation and built up a global system of alliances embracing more than forty noncommunist nations in Europe, Asia, and Latin America. In the meantime, the Soviet Union, and subsequently Communist China, supplemented its military power with that of other communist countries, allies in name but satellites in fact in that they took their orders from Moscow or Peking.

As a result of these developments, the non-aligned countries, many of them new states in Asia and Africa, came to see the rest of the world in the image of two opposing military blocs. Competition between the blocs for the support of the neutrals became a striking feature of the power struggle between the two opposing camps. Each side insisted that its alliances, no less than its armaments, were purely defensive, as has been customary throughout the ages. The claim cannot be refuted by reference to particular features of the alliances and armaments; both are instruments of policy that can serve defensive as well as offensive purposes. The claim may be belied, however, by the open and persistent assertion of foreign-policy objectives that cannot be attained except by the threat or use of military force.

Religious or ideological homogeneity has not been a traditional prerequisite of alignment among states, as demonstrated by French alliances with non-Christian Turkey in 1535, with Protestant Sweden during the Thirty Years’ War, and with the Soviet Union in 1935, as well as by alliances formed after World War II between the United States and such authoritarian regimes as Portugal, Nationalist China, and South Korea. Although domestic dissatisfaction and a loss of propagandistic advantages may arise from such heterogeneous alignments, these disadvantages are considered outweighed by strategic gains. However, the more the international conflict takes on the character of a war between transnational ideological camps, the stronger public resistance tends to become to alliances with governments of the opposing ideology. Under conditions of ideological conflict alliances may also be used to bolster regimes that share the ideology of the ally; they thereby become instruments of subtle intervention in the domestic affairs of other countries and may provoke displeasure there among political groups whose cause is harmed by such intervention.

Evaluation. Alliances have been variously praised and condemned for their effects on the community of nations and on world peace. They have been declared responsible for the power struggles among nations, although, as a rule, they are a symptom rather than a cause of such struggles. However, when a crystallization into two antagonistic blocs takes place, the race for allies coupled with the arms race may cause an intensification of the conflict and its expansion beyond the area in which it arose. In view of this danger, nations that remain unaligned and neutral may play a pacifying role as buffers or mediators and help to localize wars. In support of alliances, it can be said that they play a decisive role in the balancing-of-power process by which adequate counterpower is mustered to deter aggression. It is sometimes claimed that they also serve as stepping stones to more intimate and lasting bonds culminating in confederate or federal unity among the one-time sovereign parties. There have been cases—Germany and Switzerland offer illustrations—in which unification was preceded by wartime alliances that served to create or strengthen a sense of affinity and solidarity among the allies. Usually, however, alliances break up when the original common danger lessens or disappears; often, they break up earlier, especially if one ally sees no other way of saving itself than by capitulating to the enemy.

With the establishment of the League of Nations in 1919 and subsequently of the United Nations, the member countries seemed to have found in what has been called collective security an alternative to the traditional alliance [seeCollective security]. In practice, the hope that these universal international organizations could serve as a substitute for pacts of mutual assistance has proved to be an illusion. Nations have not been ready to fight any aggressor irrespective of their national interests.

No matter what is done to formulate an alliance treaty with care and with an eye to the interests of all the parties concerned, considerable strains within the alliance must be expected, particularly if the alliance is of long duration and goes into effect in time of peace. The interests of the allies may come to diverge even with respect to the identification of their chief enemy; conflicts among the allies may undermine their solidarity and with it their confidence in the reliability of the promises made to them by their allies. In the case of the American alliance system established after World War II special kinds of strains have materialized, particularly within the relatively tight-knit multilateral North Atlantic Treaty Organization. These strains have arisen partly because the United States alone has possessed substantial strategic nuclear forces, which have constituted the main instrument of NATO deterrence, and partly because America’s global interests could not be fully harmonized with the purely local or regional interests and perspectives of her partners.

Alliances that include major nuclear powers may run into increasing difficulties in the future. Any power committed to assist an allied victim of attack through nuclear intervention risks national suicide; its threat to accept such a risk may not be credible to the opponent and thus fail to deter him. Moreover, the nonnuclear allies lose control over their national security if it comes to rest on the independent decision of their nuclear protector. As a result, a tendency toward nuclear proliferation develops which, in turn, may have a divisive effect on existing alliances. Whether collective control of a nuclear deterrent by a group of allies is practical only the future can tell.

Although the literature on alliances considered in the abstract is not abundant, theorists in the future may expect to gain new insights into the military, psychological, and political aspects of interallied relations from two sources: first, from a wealth of specialized studies of NATO, many focused on allied nuclear policies; second, from analyses of interstate alignments employing the methodology of game theory, systems analysis, or simulation theory. See, for example, William Riker (1962) or Morton Kaplan (1957).

Most of the recent work on international integration, community building, and regionalism touches on alliances only incidentally, to suggest either that they gain in stability by incorporating a more than military identification of interest among their members or that they may serve as stepping stones toward political integration. In this connection, see Karl Deutsch et al. (1957), Amitai Etzioni (1961), and Ernst Haas (1958).

Arnold Wolfers

[See alsoCoalitions; Collective security; Containment. Other relevant material may be found underInternational politics; International relations; Isolationism; Neutralism and nonalignment.]


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Alliances are a primary form of international relations (IR) and national security policy. In conventional usage, an alliance is a formal agreement between governments to provide military support under specific political conditions. This may include military operations separately planned and executed, or highly coordinated and integrated, and other measures such as arms transfers, intelligence sharing, and the use of bases, air space, waterways, and territory. Their most important dimensions fall into three categories: (1) basic purpose and function; (2) internal politics; and (3) external affects.


The primary function of an alliance is to combine military strength against adversaries. The combined strength may be used in various ways to advance collective and individual purposes. It is most often used for deterrence, to signal to potential aggressors that they will meet such combined resistance that aggression will not pay. But it may also be used more offensively to compel others into political submission. Both of these coercive strategies, nevertheless, hinge on the most basic alliance function, to promote cooperative war fighting, for that is what makes them credible.

Although the process is never frictionless, alliances tend to form and deform in response to shifting concentrations of power and the threats they pose. Because threats are a function of intentions as well as power, compatibility of national aims tends to drive alliance patterns. Alliances may also form along lines of ideological or religious affinity, because the shared values are likely to be endangered by common threats. In late-nineteenth-century Europe, for example, a conservative alliance based on monarchical solidaritythe Three Emperors League of Prussia, Russia, and Austria-Hungaryformed against the spread of radicalism at home and abroad. Thus the political logic of combining strength against a common threat holds, even when the calculus is not determined by external power configurations alone.

When alliances fight in general wars the common interests they stand for tend to reflect status quo or revisionist goals. The former seek to uphold the prevailing territorial divisions and political frameworks of an international system. The latter seek to overthrow them. At the start of World War II, the revisionist alliance (or Axis) of Germany, Italy, and Japan joined in rejecting the League of Nations, and in pursuing territorial conquests and a new international economy. It was opposed by a status quo alliance composed of Britain and France, and their allies in Eastern Europe.

But allies purposes are often more complicated than such broad generalities suggest, for partners will also seek parochial and perhaps contradictory aims, including control over each other. Once the Soviet Union and the United States joined Britain in World War II, their Grand Alliance sought not only to eliminate enemy regimes in Rome, Berlin, and Tokyo, but also to preserve fading empire, extend new spheres of influence over satellites, and create the United Nations and a multilateral liberal economic system. There were obvious tensions among these goals, and they were amply manifest in the international politics of the cold war.


Alliances require material and/or political sacrifices. They can also multiply dangers by provoking counter-alliances and new threats. Allies will thus struggle over the distribution of the costs and benefits of their enterprise, each trying to shift obligations and dangers onto the others. Two basic organizational features shape these internal politics: the number and relative strength of the allies. Increasing the number of allies makes it harder to reconcile disparate priorities. Equality of power among allies adds to the trouble by making it harder to determine whose contributions and priorities must trump. In bilateral alliances, the internal politics are least complicated between strong and weak partners, and more complicated between roughly equal ones. In multilateral alliances of unequal partners the internal politics are yet more difficult, and most difficult of all are multilateral pacts of equals. Regardless of what form an alliance takes, each partner will try to avoid two elementary risks: The first is being abandoned by ones allies at a moment of grave danger; the second is being entrapped in a fight for an allys parochial interest that harms ones own. These twin risks pose an inherent dilemma of alliance politics, and especially during periods of international crisis, much of alliance politics reflects the strivings of each ally to navigate through it.

Although it creates the danger of entrapment, forging an alliance in peacetime is advantageous because it allows allies to send diplomatic signals and coordinate military plans and forces in ways that increase deterrence and the prospects for military victory. In principle, the more deeply allies coordinate and integrate national strategies, forces, and operations the more effective and beneficial the alliance will be. Yet even when allies agree strongly about their common political purposes, and share a high degree of trust, the business of coordinating let alone integrating military strategies, postures, and operations, can be deeply divisivewithin governments as much as between them. Traditional wisdom holds that divisions will recede as common dangers increase, and grow as common dangers fade. Thus wartime alliances tend to unravel after victory, as the Anglo-AmericanSoviet alliance did after World War II. However, the cleverest and most menacing adversaries will incite and exploit divisions within opposing alliances; then even great danger will not mute debilitating internal politics.

Important questions in IR concern the conditions for taming corrosive alliance politics. Shared norms and transparent decision-making may help liberal democracies to make and keep stronger alliance commitments. Institutionalized alliances, possessing routine processes for political decision-making and military coordination, supported by deliberative bodies and bureaucracies, may also be more robust. Such institutionalization, especially in an alliance of democracies, may even be transforming, creating an unusually cohesive security community in which partners tend to interpret and react to world politics in increasingly convergent ways. The North Atlantic Treaty Organization (NATO)the most institutionalized and democratic alliance in historymay for this reason have continued to function and adapt long after its main opponent, the Soviet-led Warsaw Pact, crumbled.


Alliances are a primary means for balancing power in international politics. Most dramatically this occurs when broad alliances form against an aggressor, like Napoleonic France, that threatens to suborn the international system. Short of such extremes, alliances may foster international order and stability by spreading deterrence and predictability among states and a sense of assurance and restraint within them. But alliances have often been seen as causing more not less international warfare. First, because competitions in alliance building can create spirals of insecurity that make war more likely. Second, because once small local wars start, alliances may widen them and make them more destructive through webs of commitments on each side. That pathology is most associated with the start of World War I in 1914 when two tight alliances, with France and Russia on one side, and Germany and Austria-Hungary on the other, became deadlocked during a crisis between Austria-Hungary and Serbia. Though both were conceived as defensive alliances to prevent war, they seem to have dragged the European powers, and much of the rest of the world, into catastrophe.

The idea that alliances promote peace and stability was boosted by NATOs cold war successes in deterring a Soviet-led Warsaw Pact attack on Western Europe, and fostering cooperation within the alliance between historical enemies West Germany and France. Expectations about reproducing the latter effect motivated NATO expansion after the cold war, when former Warsaw Pact members in Eastern Europe were left in a region of strategic uncertainty without alliance safeguards. NATOs members overcame internal disputes over the scope and pace of enlargement, and agreed to expand the alliance eastward to project stability and promote democracy within the new member states. This logic for projecting security through alliance growth thus evoked the idea that democratic alliances can instill deep bonds of common identity and security community.

In the first decade of the twenty-first century, the strongest case for such bonding remained the Anglo-American alliance: forged in world wars, it was deepened and institutionalized bilaterally and multilaterally through NATO during decades of cold war. As their security concerns shifted to nuclear proliferation and transnational terrorism, those two allies showed surprising cohesion in fighting wars in Iraq and Afghanistan. With other NATO members, however, especially concerning Iraq, there was greater political acrimony and less evident commitment to joint effort, showing that even the deeply democratic and institutionalized transatlantic security community remains vulnerable to divisive and perhaps debilitating internal politics.

As the century unfolds, two issues concerning alliances will loom largest for students and practitioners of international relations. The first is the extent to which traditional alliance frameworks can be retooled and mobilized to redress amorphous transnational terrorist threats that are less amenable to solutions based on combined military strength. The second is the extent to which traditional alliance frameworks will come into play against the largest and fastest-growing powers. Will new alliances form and tighten in reaction to preponderant American military power? Will alliances in Asia and the Pacific endure and growor whither and fractureas Chinas military posture and prestige climbs? The broad contours of twenty-first-century international politics will be defined by answers to these questions.

SEE ALSO Cold War; Confederations; Cooperation; Deterrence; Ideology; League of Nations; North Atlantic Treaty Organization; United Nations; War; Warsaw Pact; World War I; World War II


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Timothy W. Crawford

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