How Enemies Become Friends

The Sources of Stable Peace

Foreign policy analyses written by CFR fellows and published by the trade presses, academic presses, or the Council on Foreign Relations Press.

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Diplomacy and International Institutions

In his inaugural address, President Barack Obama challenged governments "on the wrong side of history" that "we will extend a hand if you are willing to unclench your fist." During his first year in office, he reached out to Iran, Russia, Cuba, and other adversaries. In How Enemies Become Friends: The Sources of Stable Peace, Council on Foreign Relations Senior Fellow Charles A. Kupchan explores when and how rivals are able to find their way to peace, arguing that "accommodation, not confrontation, is essential for successful rapprochement."

He challenges the claim that democracy is necessary for peace, demonstrating that "nondemocracies can be reliable contributors to international stability." Thus, "the United States should assess whether countries are enemies or friends by evaluating their statecraft, not the nature of their domestic institutions." In a related article in the March/April issue of Foreign Affairs, Kupchan argues that Obama confronts the double challenge of securing the cooperation of recalcitrant regimes while also facing considerable domestic opposition to the accommodation of adversaries. "Washington will have to conduct not only deft statecraft abroad but also particularly savvy politics at home," he writes.

Case studies in the book include the onset of the Iroquois Confederation in the 1400s, Anglo-American rapprochement in the late 1800s, and reconciliation between Brazil and Argentina in the 1980s.

Kupchan also underscores that efforts at rapprochement often fail, requiring that they be pursued cautiously. He addresses the breakdown of amity through historical cases such as the U.S. Civil War, the expulsion of Singapore from Malaysia in 1965, the collapse of the Concert of Europe after 1848, and the demise of the Sino-Soviet alliance after 1958.

Kupchan concludes that commercial interdependence plays only an ancillary role in reconciliation. "Deft diplomacy, not trade or investment, is the critical ingredient needed to set enemies on the pathway to peace."

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Reviews and Endorsements

Learned, lucid, [and] fascinating.

Christian Century

A rich and persuasive analysis.

Times Higher Education

Ambitious . . . delivers a powerful argument . . . . This book is entitled to serious consideration by those in the field of international relations.

The Majalla

War makes rattling good history, but peace is poor reading, Kupchan quotes Thomas Hardy as saying. Fortunately, this book manages to be an exception.

American Prospect

[A] magesterial accomplishment . . . This book will be read by scholars and policy thinkers for a very long time.

G. John Ikenberry, Foreign Affairs

Kupchan's book is fascinating, thought provoking, and consequential.

Henry Kissinger

Using historical studies of rapprochement, security community, and union as pillars for a stable world order in the twenty-first century, Charles Kupchan once again leapfrogs conventional foreign policy wisdom. He rightly foresees the elements of and a blueprint for a new global commons, one constructed of mutual interest. This is a mature work produced by a mature thinker.

Gary Hart, former U.S. senator

This is a work of admirable breadth and unusual interest. Combining an interesting theoretical framework with an extraordinarily diverse set of case studies, Kupchan has produced a lucid work that should be valued by both the academic and policymaking worlds in sorting out the relationships among classic diplomacy, democracy, and peace.

Anthony Lake, Georgetown University

In this intellectual tour de force Charles Kupchan provides a theoretically ambitious, admirably eclectic, and empirically rich account of the different worlds of international relations that are normally studied in isolation: anarchy, rapprochement, security community, and union. Statecraft not regime attributes, and politics not economic interdependence, put enemies on the pathway to peace, starting with unilateral accommodation and ending with the generation of new narratives and identities. This is a big book in every sense of the word and a major scholarly achievement.

Peter J. Katzenstein, Cornell University

Theoretically ambitious and historically audacious, How Enemies Become Friends is an invaluable and timely contribution to our understanding of the causes of war and peace. Grounded in international relations scholarship and informed by an intimate knowledge of the actual practice of international security, Kupchan's book deserves to be read by scholars and practitioners alike.

Michael Barnett, University of Minnesota

This is an extremely ambitious book about a very important topic. It delivers through a well-crafted combination of theoretical innovation and detailed case studies. Kupchan offers a powerful and carefully assembled argument that will have a substantial impact on the field of international relations.

Daniel Deudney, Johns Hopkins University

In the News

How Enemies Become Friends

World Politics Review

Excerpt Up



Long before European immigrants came to North America, Iroquois tribes settled the lands that would eventually become upstate New York. These tribes were regularly at war with each other, exacting a heavy toll on their populations. In the middle of the fifteenth century, five Iroquois tribes, ag­grieved by the mounting losses, gathered around a communal fire in the vil­lage of Onondaga in an attempt to end the fighting. The confederation they forged not only stopped the warfare, but it preserved peace among the Iro­quois for over three hundred years. Several centuries later, the Congress of Vienna served as a similar turning point for Europe. The gathering of Euro­pean statesmen in 1814–1815 not only marked the end of the destruction wrought by the Napoleonic Wars, but also produced the Concert of Europe, a pact that maintained peace among the great powers for more than three decades. Iroquois delegates resolved disputes in regular meetings of the Grand Council in Onondaga, while European diplomats preferred more in­formal congresses called as needed to diffuse potential crises. But the results were the same—stable peace.

Although the Iroquois Confederation and the Concert of Europe are now historical artifacts, both amply demonstrate the potential for diplomacy to tame the geopolitical rivalry that often seems an inescapable feature of inter­national politics. President Barack Obama appreciates this potential; he en­tered office determined not only to repair America’s frayed relations with traditional allies, but also to use America’s clout to address some of the world’s most intractable conflicts. In his inaugural address, President Obama asserted that Americans, having experienced civil war and the national re­newal that followed, “cannot help but believe that the old hatreds shall some­ day pass; that the lines of tribe shall soon dissolve; that as the world grows smaller, our common humanity shall reveal itself; and that America must play its role in ushering in a new era of peace.”

Obama wasted no time in acting on his words. Two days after assuming power, the new administration assigned high ­level emissaries the tasks of forging peace between Palestinians and Israelis and bringing stability to Afghanistan and Pakistan. As former senator George Mitchell, Obama’s choice for Middle East envoy, stated, “There is no such thing as a conflict that can’t be ended. . . . Conflicts are created, conducted and sustained by human beings. They can be ended by human beings.” Even with respect to Iran, per­haps America’s most intransigent adversary, the new administration arrived in Washington intent on opening a dialogue. The Obama administration clearly believes that enemies can become friends.

The Iroquois Confederation and the Concert of Europe are not alone in demonstrating the potential for diplomacy to produce enduring peace. At the end of the nineteenth century, for example, Great Britain deftly accommo­dated the rise of the United States, clearing the way for a strategic partner­ship that has lasted to this day. Not only did the United States peacefully re­place the United Kingdom as the global hegemon, but over the course of the twentieth century the liberal democracies of North America and Europe went on to forge a uniquely cohesive and durable political community. Al­though it formed in response to the threats posed by Nazism, fascism, and communism, the Atlantic community became much more than a military al­liance. Indeed, like the Iroquois Confederation and the Concert of Europe, it evolved into a zone of stable peace—a grouping of nations among which war is eliminated as a legitimate tool of statecraft.

It is not simply the absence of conflict that makes a zone of stable peace a unique and intriguing phenomenon. Rather, it is the emergence of a deeper and more durable peace, one in which the absence of war stems not from deterrence, neutrality, or apathy, but from a level of interstate comity that ef­fectively eliminates the prospect of armed conflict. When a zone of stable peace forms, its member states let down their guard, demilitarize their relations, and take for granted that any disputes that might emerge among them would be resolved through peaceful means. To study historical episodes in which states succeed in escaping geopolitical rivalry is to explore how, when, and why lasting peace breaks out.

In investigating the sources of stable peace, this book not only offers a dip­lomatic road map for turning enemies into friends, but it also exposes several prevalent myths about the causes of peace. Based on the proposition that democracies do not go to war with each other, scholars and policy makers alike regularly claim that to spread democracy is to spread peace. To that end, successive Republican and Democratic administrations have pursued robust policies of democracy promotion. Indeed, during the 2008 presidential campaign, influential voices on both sides of the aisle called for the establish­ment of a “League of Democracies,” a new international body that would institutionalize peace among democratic states while excluding autocracies on the grounds that they are unworthy of partnership.3 So too is thinking within both the academic and policy communities heavily influenced by the assertion that economic interdependence promotes stability. Commercial linkages between the United States and China, Israel and the Palestinian Au­thority, or Serbia and Kosovo, the prevailing wisdom maintains, promise to serve as fruitful investments in peace, not just prosperity.

This book directly challenges such conventional wisdom. It refutes the claim that democracy is necessary for peace, demonstrating that non-­democ­racies can be reliable contributors to international stability. Accordingly, the United States should assess whether countries are enemies or friends by eval­uating their statecraft, not the nature of their domestic institutions. In similar fashion, this work reveals that commercial interdependence plays only an an­cillary role in promoting peace; it helps deepen societal linkages, but only after a political opening has first cleared the way for reconciliation. Deft di­plomacy, not trade or investment, is the critical ingredient needed to set ene­mies on the pathway to peace.

These and other insights about how and when states are able to escape geo­political competition and find their way to durable peace have profound im­plications for both scholarship and policy. Understanding the phenomenon of stable peace is of paramount theoretical importance. International history is characterized by recurring and seemingly inevitable cycles of geopolitical competition and war. The emergence of zones of stable peace makes clear that conflict is neither intractable nor inescapable, pointing to a transforma­tive potential within the international system. To theorize about stable peace is therefore to advance understanding of one of the most enduring puzzles in the study of global politics: how to explain change in the character of the in­ternational system—in particular, the transformation of international anar­chy into international society.

The study of stable peace is also of obvious practical importance. Peace might be more pervasive if scholars and policy makers alike knew more about how to promote and sustain international communities in which the prospect of war has been eliminated. Why and how did peace break out among the United States and Great Britain, Norway and Sweden, the founding mem­bers of the Association of Southeast Asian Nations (ASEAN), and the no­madic tribes that now constitute the United Arab Emirates? What lessons can be drawn for fashioning zones of peace between China and Japan, Greece and Turkey, or other contemporary rivals? In the Middle East and Africa, regional institutions have the potential to help dampen rivalry and prevent war, but they have yet to mature. What can be done to advance the prospects for stable peace in these regions?

Another priority for policy makers is preserving existing zones of peace, the durability of which can by no means be taken for granted. Following the end of the Napoleonic Wars in 1815, the Concert of Europe succeeded in se­curing peace among the great powers for over three decades. By 1853, how­ever, Europe’s major powers were again at war—this time in the Crimea. The Soviet Union and China forged a remarkably close partnership during the 1950s; by the early 1960s, they were open rivals. The United States enjoyed more than seven decades of stable and prosperous union among its indi­vidual states, only to fall prey to a civil war in the 1860s. The United States survived the challenge to its integrity, but other unions have not been as fortunate. The Soviet Union, Yugoslavia, the Senegambian Confederation, Czechoslovakia—these are only a few of the many unions that are today his­torical artifacts.

The fragility of former zones of peace makes clear that comity among the Atlantic democracies can by no means be taken for granted. Indeed, since the Cold War’s end, transatlantic tensions have mounted over a host of issues, including ethnic violence in the Balkans, the invasion of Iraq in 2003, and the ongoing conflict in Afghanistan. Amid the rift that opened over the Iraq war, Europeans began to question whether they could still look to the United States to provide responsible international leadership. In turn, Americans began to question whether they should continue to support European unity, suspecting that the European Union (EU) was gradually transforming itself from a partner into a rival. The Atlantic community is still a zone of stable peace—armed conflict among its members remains unthinkable—but geopo­litical competition, even if only in subtle form, has returned to relations be­tween the United States and Europe.

The challenge for contemporary statecraft entails not just preserving exist­ing zones of stable peace, but also deepening and enlarging them. The EU continues to seek more centralized institutions of governance even as it extends its reach to the south and east, exposing new members to its peace­ causing effects. ASEAN’s membership has also grown, taxing the body’s ca­pacity to coordinate regional diplomacy. South America has of late enjoyed advances in cooperation on matters of commerce and defense, but the deep­ening of regional integration still faces significant obstacles. These experi­ments in taming geopolitical rivalry are far from complete.

Fashioning stable peace among the great powers is another key challenge. With the European Union, China, Russia, India, Brazil and others on the rise, major changes in the distribution of power promise to renew dangerous competition over position and status. It may well be, however, that shifts in the global balance need not foster great-power rivalry. The history of the Concert of Europe yields important lessons about how to forge cooperation among major powers—but also sobering warnings about how easily such co­operation can erode. Rapprochement between the United States and Great Britain demonstrates that hegemonic transitions can occur peacefully—but it represents the only case of peaceful transition on record. Examining the Concert of Europe, the onset of Anglo-­American rapprochement, and other instances of stable peace thus promises to elucidate the opportuni­ties—as well as the challenges—that will accompany the onset of a multipo­lar world.


Two puzzles motivate and guide this study. First, through what pathway do states settle outstanding grievances, dampen geopolitical competition, and succeed in constructing a zone of peace? What is the sequential process through which enemies become friends? Second, under what circumstances do zones of stable peace form? What causal conditions enable stable peace to emerge and endure?

Stable peace breaks out through a four-­phase process. Reconciliation be­gins with an act of unilateral accommodation: a state confronted with multi­ple threats seeks to remove one of the sources of its insecurity by exercising strategic restraint and making concessions to an adversary. Such concessions constitute a peace offering, an opening gambit intended to signal benign as opposed to hostile intent. Phase two entails the practice of reciprocal re­straint. The states in question trade concessions, each cautiously stepping away from rivalry as it entertains the prospect that geopolitical competition may give way to programmatic cooperation.

The third phase in the onset of stable peace entails the deepening of soci­etal integration between the partner states. Transactions between the parties increase in frequency and intensity, resulting in more extensive contacts among governing officials, private ­sector elites, and ordinary citizens. Inter­est groups that benefit from closer relations begin to invest in and lobby for the further reduction of economic and political barriers, adding momentum to the process of reconciliation.

The fourth and final phase entails the generation of new narratives and iden­tities. Through elite statements, popular culture (media, literature, theater), and items laden with political symbolism such as charters, flags, and anthems, the states in question embrace a new domestic discourse that alters the iden­tity they possess of the other. The distinctions between self and other erode, giving way to communal identities and a shared sense of solidarity, complet­ing the onset of stable peace.

As to the causal conditions that enable enemies to become friends, stable peace emerges when three conditions are present among the states in ques­tion: institutionalized restraint, compatible social orders, and cultural com­monality. Institutionalized restraint is a favoring but not necessary condition, whereas compatible social orders and cultural commonality are necessary conditions. The causal logic at work is as follows.

States that embrace institutionalized restraint possess political attributes that make them especially suited to pursuing stable peace. Governments that accept restraints on their power at home are most likely to practice strategic restraint in the conduct of their foreign relations. The exercise of strategic restraint and the withholding of power reassure potential partners by com­municating benign intent and dampening rivalry. The practice of strategic restraint is most pronounced among liberal democracies; the rule of law, electoral accountability, and the distribution of authority among separate institutions of governance serve as potent power­-checking devices. Liberal democracy, however, is not a necessary condition for stable peace. Other con­stitutional orders regularly practice strategic restraint.6 Constitutional mon­archies, for example, institutionalize checks on unfettered power and thus exhibit political attributes favorable to stable peace. Moreover, the cases will reveal that even autocratic states, which lack institutionalized checks on power, at times practice strategic restraint. It follows that whereas the prac­tice of strategic restraint is a necessary condition for stable peace, the pres­ence of institutionalized restraint is not. Accordingly, regime type alone does not determine the suitability of a state for pursuing stable peace.

The emergence of stable peace also depends upon the presence of compat­ible social orders. As the states engaged in building a zone of peace proceed with political and economic integration, the societies involved interact with greater frequency and intensity. If their social structures are compatible, inte­gration reinforces existing political and economic elites—and proceeds apace. If their social orders are incompatible, integration upsets and threatens patterns of authority in one or more of the parties, provoking domestic coali­tions that block further advances toward stable peace. The following dimen­sions of social order are of particular salience: the distribution of political power among different social classes; the distribution of political power among different ethnic and racial groups; the organizing principles of economic production and commercial activity.

The third condition making stable peace possible is cultural commonality. Culture refers to an interlinked network of practices and symbols based pri­marily on ethnicity, race, and religion. Reciprocal perception of cultural commonality is socially constructed, a product of a changing repertoire of prac­tices and symbols, not a matter of primordial and fixed identities. Peoples that see themselves as ethnically or religiously incompatible can, as the product of reconciliation, eventually come to see themselves as ethnic or religious kin. At the same time, narratives of compatibility and similarity are easier to generate among certain populations than others. The cultural barriers between Protestants and Catholics may be more readily overcome than those between Christians and Muslims. As Britain searched for potential partners in the late nineteenth century, it sought to improve relations with both the United States and Japan. Anglo-­Saxon commonality provided a strong sense of cultural affinity between Britons and Americans, a factor that facilitated the onset of lasting rapprochement. In contrast, a narrative of commonality was not readily available between Britons and Japanese. Indeed, a sense of cultural difference ultimately came to stand in the way of a durable partner­ship between Britain and Japan.

From this perspective, the causal relationship between cultural commonal­ity and stable peace comes close to that of social selection. When searching for potential partners in peace, states are drawn to other states with which a narrative of common heritage is more readily available. Cultural commonal­ity is even more important during the later stages of the onset of stable peace. When elites seek to consolidate stable peace through the generation of a narrative that propagates a sense of communal identity, they have at their dis­posal preexisting recognition of cultural bonds.

Cultural commonality is no guarantee of compatibility; states sharing a common heritage are often bitter rivals. But it does facilitate the onset of stable peace, both at its onset and its completion. It is also the case that the notion of a common culture is elusive—one that, as mentioned above, is mal­leable and often the product of political and social construction rather than primordial characteristics. The notion’s malleability notwithstanding, the cases demonstrate a strong correlation between perceptions of cultural com­monality and stable peace.


Zones of stable peace can take three different forms—rapprochement, secu­rity community, and union. Rapprochement is the most rudimentary form of stable peace. Long-­standing adversaries stand down from armed rivalry, agree to settle their disputes amicably, and ultimately develop mutual expec­tations of peaceful coexistence. A security community is a more evolved form of stable peace. It is a grouping of two or more states that institutionalize a set of norms and rules in order to manage peacefully their relations. A union is the most mature form of stable peace. It is a grouping of two or more states that merge into a single political entity, minimizing, if not eliminating, the geopolitical consequence of preexisting borders.

Each of these three types of stable peace is examined through an extensive set of historical case studies. Numerous considerations shaped the selection of cases. The empirical chapters examine successful cases as well as failures— that is, historical episodes in which stable peace forms as well as those in which it breaks down.7 Such variation in outcomes is needed to help identify the con­ditions under which stable peace takes root and endures. In addition, examin­ing successes and failures enables this book to speak more directly to the pol­icy agenda by offering insight into measures aimed at encouraging new zones of peace as well as at preserving and extending existing ones. The cases were also selected to ensure wide variation on the main explanatory variables—re­gime type, compatibility of social orders, and cultural commonality—in an effort to isolate the causal role played by these different variables and the feed­ back mechanisms that exist among them. For similar reasons, the cases exhibit substantial variation across geographic region and historical period.

The successful and failed instances of stable peace examined in this book thus represent a diverse subset of a broader universe of cases. In addition, especially because the literature on this topic is still evolving, preference was given to examining a wide range of cases in less depth rather than examining a few cases in greater depth. This preference for breadth rather than depth enables the book to probe more effectively similarities and differences across cases and to spot patterns that would emerge only by examining historical episodes that traverse a broad temporal and geographic span. More cases, even if covered in less detail, lend the theory-­building enterprise the reliabil­ity of a larger sample.

These considerations structure the historical chapters that follow. Chapter 3 contains an in-depth examination of a single case of rapprochement—that of the United States and Great Britain between 1895 and 1906. This exten­sive case study helps strike a balance between the richness that comes with a close investigation of a critical case and the rigor afforded by a larger set of case studies. As a result of devoting an entire chapter to this single case, rapprochement receives more comprehensive coverage than either security com­munity or union. This bias stems from the observation that it is amid rap­prochement that the processes through which states move from rivalry to stable peace are most active and consequential. Along the continuum from anarchy to union, more variance in interstate relations occurs in the transfor­mation from unfettered rivalry to rapprochement than occurs amid the move from rapprochement to security community and/or union. Once rapproche­ment has been achieved, the advance to security community or union entails a furthering of processes that have already had transformative consequences; much of the work has already been done. In this sense, the “kernels” to un­derstanding stable peace may well be embedded in the core mechanisms that drive rapprochement. Security community and union, more evolved forms of stable peace with more extensive social character, then build on and deepen these core processes.

Careful study of a single case is also necessary to acquire a detailed under­standing of the complicated processes through which strategic interaction, domestic politics, and ideational change interact to produce stable peace. Historians have examined the U.S.­ British case extensively; the wealth of ex­isting sources makes it an especially attractive candidate for in­-depth study. Admittedly, such reliance on this one episode of rapprochement runs the risk that a single case weighs too heavily in the enterprise of theory construction. However, running this risk seems warranted, if not necessary. At this early stage in building a body of theory on stable peace, it is important to capture the richer and more textured insights yielded by close reading of a critical case study.

Chapter 4 contains four additional case studies of rapprochement. Two episodes of successful rapprochement are examined: Norway and Sweden from 1905 to 1935, and Argentina and Brazil from 1979 to 1998. The two cases of failed rapprochement are: Great Britain and Japan from 1902 to 1923, and China and the Soviet Union from 1949 to 1960.

Chapter 5 contains five case studies of security community. The three suc­cessful cases examined are: the Concert of Europe from 1815 to 1848; the European Community (EC) from 1949 to 1963; and the Association of Southeast Asian States (ASEAN) from 1967 through the present. The two failed cases are: the breakdown of the Concert of Europe between 1848 and 1853, and the Gulf Cooperation Council (GCC) from 1981 through the present.

Chapter 6 contains five main case studies of union. Three successful cases of union are examined: the Swiss Confederation from 1291 until 1848; the Iroquois Confederation from 1450 to 1777; and the United Arab Emirates (UAE) from 1971 through the present. The two cases of failed union are: the United Arab Republic (UAR) from 1958 to 1961, and the Senegambian Con­federation from 1982 to 1989. The conclusion to chapter 6 examines in a more cursory fashion three additional successful cases: the unification of the United States (1789), Italy (1861), and Germany (1871); and two additional failures: the U.S. Civil War (1861) and the expulsion of Singapore from Malaysia (1965). This selection of case studies is summarized in table 1.1.

No single story emerges from examination of these cases. Rather, each in­stance of the formation or dissolution of a zone of stable peace follows its own unique pathway and takes place amid a unique set of circumstances. Nonetheless, recurring patterns do emerge, both as to how stable peace breaks out and as to the causal conditions that bring it about. The argument summarized above and fleshed out in the next chapter represents a distilla­tion of the complex process that transforms enemies into friends; it is a pre­cise account of none of the cases, but a generic account of all of them. The goal is to locate the common thread that unites the disparate cases, and in so doing to discover the mechanisms and conditions enabling states to escape the imperatives of geopolitical competition. The same caveats apply to the historical cases focusing on the unraveling of stable peace. When a zone of peace unravels, the process through which friends become enemies operates in reverse; narratives of opposition prompt societal separation, which in turn degrades cooperation, ultimately awakening geopolitical competition. And it is the absence of the key causes of stable peace—institutionalized restraint, compatible social orders, and cultural commonality—that explains these cases of failure. Nonetheless, each instance of the collapse of stable peace takes place through its own pathway and occurs under a unique set of circumstances.

Moreover, the following chapters examine only a sample of cases; other instances of the onset and collapse of stable peace may take an altogether different path. Accordingly, this study does not purport to develop and test a determinate model or to make predictive claims about when and where spe­cific zones of peace will form or fail. Rather, it offers scholars a framework and policy makers a guide for addressing how and why enemies become friends and for identifying the conditions that facilitate the emergence and endurance of zones of stable peace.


This book addresses dual audiences. It speaks to the mainstream theoretical concerns of scholars, seeking to advance academic debate about global poli­tics. It simultaneously seeks to contribute to ongoing debates within the pol­icy community. In this latter regard, the book develops five principal argu­ments that have direct implications for the conduct of foreign policy.

First, engagement with adversaries is not appeasement; it is diplomacy. Long-­standing rivalries end not through isolation and containment, but through negotiation and mutual accommodation. Under the appropriate cir­cumstances and through skillful diplomacy, enemies can become friends. En­gagement does not always succeed in bringing geopolitical rivalry to an end—as many of the historical case studies in this book make clear. But it does have the potential to do so. Accordingly, policy makers should give sta­ble peace a chance.

Second, democracy is not a necessary condition for stable peace. As men­tioned above, the conventional wisdom within the U.S. foreign policy com­munity is that lasting peace is the unique provenance of liberal democracies. The analysis in this book, however, rejects the proposition that liberal de­mocracies alone are suited to fashioning zones of peace. Autocracies are ca­pable of building lasting partnerships with each other as well as with democ­racies. Accordingly, the United States should base its relations with other states primarily on the nature of their foreign policy behavior, not the nature of their domestic institutions.

Third, the onset of stable peace is about politics, not economics. Academ­ics and policy makers alike often attribute the onset of peace to economic and societal interdependence; societal interaction supposedly clears the way for political reconciliation. In contrast, this book argues the opposite—polit­ical reconciliation must come first if societal interaction is to have beneficial geopolitical consequences. Only after political elites have succeeded in tam­ing geopolitical competition do the pacifying effects of economic interdepen­dence make a major contribution to the onset of stable peace. The break­throughs that lead to stable peace are strategic rather than economic in nature. Diplomacy, not trade or investment, is the currency of peace.

Fourth, compatible social orders are a key facilitator of stable peace, while incompatible social orders are a key inhibitor. Among states with contrasting social orders—aristocratic versus egalitarian, industrial versus agrarian, economically open versus protectionist—the societal integration that follows from political reconciliation threatens privileged social sectors, causing them to block further movement toward stable peace. It follows that policy makers should pay more attention to social order than regime type when assessing the suitability of a potential partner. It also follows that policies aimed at so­cial change and convergence are more likely to promote peace than policies aimed exclusively at democratization.

Finally, cultural commonality plays an important role in determining the potential for and durability of stable peace. Policy makers therefore need to take cultural factors into consideration as they seek to expand existing zones of peace and create new ones. There is nothing primordial or essentialist about cultural dividing lines; societies that see one another as culturally dis­tant can over time come to see one another as sharing a communal cultural identity. There are, however, constraints on the malleability of such identities. The availability of a narrative of commonality gives some zones of peace a greater chance of success than others; states that enjoy a preexisting ethnic or religious commonality will find it easier to construct a shared identity than those that do not. Policy makers should by no means interpret this finding as confirmation of the proposition that different civilizations are destined to clash. But they should recognize that states that enjoy a preexisting sense of common heritage are better candidates for stable peace than those that do not. They should also appreciate the importance that narratives of cultural commonality can play in promoting peace—especially among culturally di­verse groupings of states.

The following chapter lays out the book’s conceptual foundations in greater detail and explores the causes of stable peace in more depth. Chapters 3 through 6 contain the historical case studies, examining in turn rapproche­ment, security community, and union. The final chapter draws theoretical conclusions and elaborates on the policy implications of the study.