Early modern efforts to justify warfare entailed serious reflection on the relationship between Christianity and nature or natural law. Those working in a Thomist tradition could draw on a concept of natural law as an ethical system distinct from Christianity; others rejected that concept, working instead to show that warfare could form part of the duties of Christians. All sides recognized the tension between the words of Christ and the demands of human political life, especially when it came to defending military activity. That tension produced creative discussions of natural law, political thought, and theology, in the universities and beyond.