Cohrs's book, The Unfinished Peace after World War I, provides a new account of the period following the Versailles Treaty. He addresses the question of why the European system did not reach a sustainable equilibrium during the interwar period. Standard accounts of the time period typically assume that the Versailles Treaty set up European states for failure. But, in fact, Cohrs demonstrates convincingly that significant efforts to achieve stability did not end with Versailles, particularly as the Franco-German question remained unresolved in the 1920s. The 1924 London reparations settlement and the 1925 Locarno security pact were instrumental in reorienting the efforts of Versailles into a “real” peace settlement. The body of the research is focused on the period from 1924 to 1929, an often-overlooked but critical time period. One of the main arguments of the book is that British and American policy makers generated ideas that affected the seemingly obstinate preferences of their French and German counterparts. Ultimately, the failure of the interwar states system was not inevitable as balance-of-power scholars have argued.

Cohrs takes a refreshing and well-balanced perspective, striking a reasonable compromise between a variety of historical approaches. He provides a methodological road map for understanding the period more generally, in such a way that the agency of individuals, domestic cultures, and the structure of the international system are all taken into account. Thus, his study not only reveals a wide range of primary sources that bring to light a convincing revisionist interpretation of the early interwar period, but it also makes an important statement about the climate of international relations at the time. In this regard, he argues that “realism” cannot account for the outbreak of World War II because it was not simply a result of the breakdown of the balance of power. In other words, the explanation is not structural. Cohrs chooses instead to focus on the individual level of analysis, and particularly on a core group of elites who were influential in spreading ideas transnationally. These individuals include Ramsay MacDonald, Charles E. Hughes, Austen Chamberlain, Frank B. Kellogg, and Herbert Hoover, among others.

Together these elites formed a veritable transnational network of “norm entrepreneurs” and generated powerful ideas, which ultimately had an impact on international relations at the time. The outcome fell short of success, but a close look at the lives of these individuals paints a very different picture than one has come to expect. American and British policy makers engaged in a rich and dynamic dialogue, learned lessons from past mistakes, and were persuaded occasionally to change their minds. There was also a tendency at the time for the British and Americans to exercise a division of labor, with the former focused on security issues and the latter concerned with economic issues.

According to Cohrs's account, the role of these individuals reached beyond each other and the international system to the domestic level. In contrast to the realist approach, Cohrs shows that domestic politics matter, part of the reason that London and Locarno could not ultimately withstand a major crisis. With the rise and consolidation of democracy, the policies supported by the elites had to be workable in the international system, as well as legitimated at the domestic level. These influential policy makers were each playing an important part in redefining his country's role in the international system.

Thus, Cohrs proposes a new concept to replace “balance of power,” which he calls “legitimate equilibrium.” It involves “balance of rights, security, reciprocal satisfactions and responsibilities within the international system—a balance deemed legitimate and fundamentally fair not only by international policymakers but also by those on whose domestic support their policies depended” (14). Cohrs makes this point persuasively, although it is not the major contribution of the study. Rather, this book's greatest contribution lies in its rich documentation and its detailed look at individuals who were constrained by the structure of geopolitics but at the same time had autonomy for action by virtue of the strength of their shared norms and ideas. They had to follow the rules of the game, but they were also willing to accept changes to the framework.

The book is divided into three parts in addition to a prologue and an epilogue. The prologue provides an account of the aftermath of the Treaty of Versailles and emphasizes the extent to which its design for postwar order was unsustainable. Part 1 introduces the policy makers who replaced Woodrow Wilson and Lloyd George and discusses the Dawes plan and London settlement. The second part elucidates the mid-1920s shifts in focus to the perspective of the French and German leaders, showing how they were impacted by Anglo-American policies. After shedding light on the successes of the early to mid-1920s and on the impact of Anglo-American ideas on European security, the third part shows that all of this was nonetheless undermined in the face of the crisis of the Great Depression. Finally, the epilogue brings us to the early 1930s, the collapse of the Weimar Republic, and the rise of Hitler.

By focusing on the extent to which peace was achieved rather than on the multitude of factors leading to the breakdown of peace, Cohrs reveals an important dimension of the role of diplomacy at the time. If anything, it was the success of London, Locarno, and the Anglo-American agenda that led to the system's ultimate failure. Diplomacy went far but not quite far enough, and this became apparent only when crisis struck in the form of the Great Depression. The eventual collapse of the system can be explained not because of any weakness in the London and Locarno agreements themselves but, above all, because policy makers’ efforts fell short in sustaining them. Cohrs's book details this dynamic with a striking array of primary sources from archives in Great Britain, Germany, the United States, and France. Though a lengthy volume, it is a masterpiece of research and one that should significantly change the way we see the interwar period.