ABSTRACT
Western Christianity became dominated by a different tradition. The early collapse of the western empire did not allow Byzantine triumphal rulership to take root; and St. Augustine, who wrote his City of God to explain the sack of Rome in A.D. 410, deliberately set the Latin churches on a separate track. Throughout the Middle Ages, the writings of Augustine remained the most important influence on western European thinking about warfare. The continuous history of just war doctrine began about 1140 with the Decretum of Gratian, the basic compilation of canon law, which discusses the morality of warfare in its Causa 23. Christian emperor Gratian quoted there the definitions of a just war by Cicero and by Augustine. Medieval discussions commonly recognize the causes mentioned in Gratian. The problem of right intentions produced the most lasting medieval contribution to just war theory. The first crack in the medieval synthesis appeared in Italy around 1400, with the rise of "civic humanism".
