Imminent violence and war make news headlines, while longstanding peace and good inter-state relations hardly seem newsworthy. By contrast, Charles Kupchan's new book, How Enemies Become Friends: The Sources of Stable Peace, focuses on the origins of peace rather than war. While war is certainly big news, he posits that the bigger news is that the US-Canada border has been consistently peaceful for more than a century, or that only 68 years after France and Germany fought two world wars, people can now drive across the border as though it does not exist. His new book seeks to identify the dynamics that lead countries to achieve lasting peace.

The book covers 20 cases since the 13th Century in which previously warring states established some measure of peace. In order to evaluate the level of peace, Kupchan marks each stage in the evolution from rapprochement (in which states live in peaceful coexistence), to security community (where borders matter, but peace between states is insured through treaties), to union (in which states create a political formation in which borders become insignificant).

From the cases he examined, Kupchan concluded that movements from hostility to peace always begin with a conciliatory act which is brought about not by altruism but by strategic necessity. For example, in the 1890s strained relations between Great Britain and the U.S were at risk of deteriorating over a border dispute between Venezuela and British Guyana. On the basis of the Monroe Doctrine, the U.S. demanded that the British take the dispute to arbitration. Although Britain had not previously recognized the Monroe Doctrine, flashpoints in various parts of its empire threatened to overextend its forces and yet another confrontation with the U.S. was beyond its capacity. Due to this strategic necessity, therefore, the British agreed to arbitration and decided to recognize the Monroe Doctrine. This act of good will launched a sequence of events that led to a change in interstate relations: within 11 years, war between the U.S. and Great Britain was considered fratricide.

The lesson gleaned from these 20 case studies is that peace does break out and that war is escapable. Kupchan's research shows that engagement is not appeasement, but sometimes leads to peace. According to him, if there is a magic potion that leads to peace, it is the practice of strategic constraint: the readiness of powers to back down dictates how easily war will be avoided. The book also debunks the conventional wisdom that regime type matters (democracies do not fight with other democracies) and interstate trade and economic interdependence secures peace. Rather, Kupchan suggests that in order to build lasting peace, states must create conditions in which strategic constraint is possible, either by doing something irreversible to limit its power or by co-binding, in which two or more countries tether together their resources so that one cannot use it against the other.

In her comments, Martha Finnamore noted that political science and international relations have been active in focusing on why wars break out, but have been largely silent on the absence of war. Moreover, these disciplines have poor tools for explaining change over time. She praised the book for attempting to overcome these methodological limits, and especially for Kupchan's willingness to ask a big, important question. She offered a condensed version of Kupchan's theory: states make peace when they practice restraint, when there is cultural compatibility and when social order in both states is similar. Finnamore began the discussion by asking, if one of these elements is missing, how can you set a process toward peace into motion? She also raised the issue of judgment: how do leaders know when they have reached the point in which conciliation is a strategic necessity? The virtue of the book, she concluded, is that its convincing arguments and engaging examples left her with a lot to think about.

Christian Ostermann, Director of European Studies