 As the title of his magnum opus implies, the normative status of war was of paramount concern to Grotius. The common distinction between ius ad bellum and ius in bello—the distinction between the rightful causes of war versus the rightful conduct of war—is useful for understanding his views. Regarding ius ad bellum, Grotius devotes DIP Chap. Three and DIB I.2 to the question of whether it is ever lawful to wage war. He argues that war is not only compatible with but sometimes compelled by all three major kinds of law—the law of nature, the law of nations or international law, and divine law. In support of his answer, he adduces a number of conceptual, historical and theological arguments. It would be tendentious to recount all of them, so take just one influential example of the first sort: