From Just War to Modern Peace Ethics This book rewrites the history of Christian peace ethics. Christian reflection on reducing violence or overcoming war has roots extending back to ancient Roman philosophy and it eventually decisively influenced the formation of modern international law. This study traces the development of the tradition from Cicero Augustine and Thomas Aquinas to early modern thinkers including Vitoria Suarez Martin Luther Hugo Grotius and Immanuel Kant. These sources influenced modern peace ethics cosmopolitanism and international law based approach as can be found in the late Pope John Paul IIs peace teaching. Heinz Gerhard Justenhoven Institute for Theology and Peace Hamburg Germany; William A. Barbieri Jr. The Catholic University of America Washington DC USA.