As it transitioned from its late medieval into its early modern forms, the Christian just war tradition did more than shape colonialization, law, and the nation-state; it significantly shaped modernity itself. Its emphases on four big modern ideas – autonomy, immanence, instrumentalism, and universalizability – manifest throughout the modern social imaginary, including in the way both religion/theology and the nonhuman natural world are removed from view in the political realm. Viewing this transition through explicitly theological lenses helps make sense of modernity’s preoccupation with (state) violence, its struggles to negotiate ambiguity, and its commitment to a myth of progress that conceals the ironies, disjunctions, and ambivalences of history. It also helps to explain why modern political thought ignores the nonhuman natural world at a time when the costs of such ignorance are growing exponentially.