At a time when many alliances are being called into question, this volume considers the present and historical realities of the global U.S. alliance network. Ironclad contributes to the scholarly, political, and policy debate on alliance theory, examining the theoretical underpinnings of why states align, the effects of nuclear weapons on alliance alignment, and the implications of the cyber domain for alliances. Ironclad further informs the reader on the practice of alliance management in the twenty-first century, with studies of the U.S. alliance system in Asia and Europe. Sure to be of use to scholars, students, and policy practitioners alike, Ironclad is a definitive examination of the value and role of alliances in the twenty-first century.