Asia's Evolving Security Architecture Ralf Emmers (bio) In Asia's Regional Architecture: Alliances and Institutions in the Pacific Century, Andrew Yeo makes both a conceptual and empirical contribution to the existing literature on the evolving architecture in Asia since the end of World War II. The scholarship on the subject is vast and comprehensive, but it tends to be divided into two sets of approaches that have characterized the international relations of the region: on the one hand, bilateral alliances and other defense ties linking various Asian states to the United States, and on the other, multilateral arrangements mostly driven by the Association of Southeast Asian Nations (ASEAN). Moreover, the existing literature on the regional architecture has been further divided along economic and security lines, as only a few publications have so far explored the security-economic nexus in Asia. Finally, the literature on the regional architecture is dominated theoretically by constructivism (with its emphasis on norms and community-building) and realism (with its focus on hard and soft balancing). Asia's Regional Architecture is insightful and ambitious. It seeks to bridge the different examples of bilateralism and multilateralism that together form the regional architecture as well as to cover both the economic and security sides of the overall cooperative framework in the region. The empirical evidence is well-known, as bilateralism and multilateralism in Asia have been extensively researched since the end of the Cold War. Other sources have looked at Asia's multilateral architecture in a topical and timely fashion, especially with the architecture's ongoing buildup and rapid evolution. It is true, therefore, that the empirical evidence presented in Asia's Regional Architecture is not particularly new. Yeo contributes to the literature by bringing all of this material together and analyzing it through the application of a less well-known conceptual framework—historical institutionalism. To my knowledge, this has never before been attempted, making the book both original and innovative. The end result is that Asia's Regional Architecture takes a long-term view that enriches the existing analysis and provides a sense of perspective. [End Page 128] The book makes two significant contributions to the existing literature. First, scholarship has for too long studied the hub-and-spoke system and the ASEAN model of cooperative security separately and independently from each other. The author fills this lacuna by exploring the synergies between bilateralism and multilateralism in a historic and systematic way. Second, Yeo goes beyond the standard realism-constructivism debate that has dominated academic discussions of Asian architecture since the 1990s. Historical institutionalism, with its notions of endogenous change, institutional layering, and institutional drift, offers a convincing framework to explain stability and change in the regional architecture. Though some of this has been attempted before on a smaller scale, this book is comprehensive in its attempt to fulfill these objectives. Indeed, Yeo provides a rich, systematic, and detailed account of how the security and economic architecture has evolved since 1945. The importance given to providing a coherent conceptual framework that ties all this empirical evidence together is therefore critical. Furthermore, Asia's Regional Architecture is well-researched. Yeo thoroughly reviews the existing conceptual and empirical literature. He comfortably switches from an in-depth discussion on historical institutionalism to illustrations of economic and security regionalism. Chapter 1 sets the stage by introducing methods and research design and articulating a series of propositions. The structure of the book flows logically and its organization is clear and well-conceived, with the chronological approach adopted in the chapters preventing too much repetition of empirical evidence. The overall writing style is coherent and engaging. Some issues should be mentioned, however. First, as most of us do, Yeo struggles to make sense of the Trump administration and its position on the regional architecture, among other areas of its foreign policy. The book mostly ends with the Obama administration, although the concluding chapter touches on the "America first" principle and Trump's decision to withdraw from the Trans-Pacific Partnership. Trump has so far shown little interest in Asia's architecture, especially in comparison to the Obama administration and its policy of a pivot toward Asia. The wider issue of a possible...