'Just War' doctrine has been a feature of Christianity since ancient times. But can a war ever be just? Addressing the 'just war' concept from its formulation in the writings of Saints Augustine and Thomas Aquinas, through Patristics, the Catechism of the Catholic Church, the Compendium of the Social Doctrine of the Church, and the writings of modern Popes including Saint John XXIII and his landmark encyclical Pacem in Terris, this book outlines the slow, but steady, movement away that has taken place from the original concept as postulated by the Scholastics. It also presents the conclusions of postmodern Christian leaders on 'just war' including those of Pope Francis, the Patriarch Bartholomew I, and the 2017 Vatican first-ever conference on the subject.