Many continue to believe that the United States is a nation of political moderates. In fact, it is a nation divided. It has been so for some time and has grown more so. This book provides a new and historically grounded perspective on the polarization of America, systematically documenting how and why it happened. It presents commonsense benchmarks to measure polarization, draws data from a wide range of historical sources, and carefully assesses the quality of the evidence. Through an innovative and insightful use of circumstantial evidence, it provides a much-needed reality check to claims about polarization. This rigorous yet engaging and accessible book examines how polarization displaced pluralism and how this affected American democracy and civil society. No subject is more central to understanding American politics than political polarization, and no other book offers a more in-depth and comprehensive analysis of the subject than this one.