Military pension policies are as old as the republic itself and reside at the intersection of American social, economic, and defense policy. But as the nation's social and economic circumstances underwent dramatic changes over the last half-century, military pension policy remained static, stuck in the personnel and retirement model of the industrial age. This book examines why. Integrating policy history, theory, and practice, Twenty Years of Service provides the most comprehensive examination of US military pension policy in a generation. Brandon J. Archuleta sets the stage with an exploration of the rise, evolution, and transformation of the veterans' policy subsystem from the American Revolution through World War II. The ensuing theoretical overview explains how the military personnel policy subsystem achieved the autonomy it enjoyed from 1948 to 2018; it also offers a new perspective on autonomous policy subsystems in general, which helps to account for the long-term pension policy stasis. In practical terms, Archuleta explores the role of the successful 2015 Military Compensation and Retirement Modernization Commission as an institutional venue for policy change during the congressional budget battles of the 2010s. Through extensive archival research, illustrative case studies, and field interviews with Pentagon bureaucrats, congressional staffers, veterans' lobbyists, defense scholars, and journalists, Twenty Years of Service brings the policymaking process to life. Its insights will prove invaluable to policy scholars and defense practitioners alike.