In this essay, I compare two pioneer thinkers of the “just war” tradition across cultures: Gratian in the Christian tradition, and Mengzi (Mencius) in the Confucian tradition. I examine their historical-cultural contexts and the need for both to discuss just war, introduce the nature of their treatises and the rudimentary theories of just war therein, and trace the influence both thinkers’ theories have had on subsequent just war ethics. Both deemed just cause, proper authority, and right intention to be necessary (...) conditions for initiating a just war. However, Gratian’s theory has a presumption against injustice whereas Mengzi’s theory has a presumption against war. As a jurist of the Church, Gratian sought to discriminate just from unjust wars, while Mengzi, a moral-political advisor to rulers, was more concerned with avoiding bloodshed and building lasting peace. In addition to examining these thinkers’ respective historical influences, I submit that Gratian’s Decretum and the Mengzi are pioneering in two more senses. First, they offer important clues to understanding how just war ideas were developed very differently in medieval Europe and in premodern China. Second, both embodied features that helped shape their subsequent intellectual tradition, which in turn molded the different legacies of these two works. (shrink)