Summary A good deal of the late-twentieth-century commentary on Kant's ‘Perpetual Peace’ essay accepted its author's view that his conception of cosmopolitan justice had superseded the law of nations, some of whose leading exponents—Grotius, Pufendorf, and Vattel—Kant characterised as ‘miserable comforters’. Focusing on the case of Vattel, in this paper I begin to subject Kant's claim to an historical investigation, asking whether his ‘Perpetual Peace’ did indeed supersede Vattel's Law of Nations in terms of the actual uses of the texts in a variety of historical contexts. In pointing to an array of evidence against Kant's widely accepted claim, I develop a different and more historical way of assessing the relation between the two writers. Kant, I argue, should be approached as a political metaphysician whose conception of cosmopolitan justice formed part of a factional theological and philosophical attack on the law of nations tradition. Vattel, however, was a diplomatic official whose text operates within the horizon of the European state ensemble and functioned as a summative abstraction of a wide variety of post-Westphalian public-law treaties and diplomatic rules and conventions. This accounts for the wide distribution, use, and influence of Vattel's work in a variety of Anglophone contexts from the late eighteenth century through to the end of the nineteenth, where Kant's text was marginal to discussion.