The turn of the nineteenth century is widely seen in histories of international law as a watershed moment, when the naturalism of the eighteenth century paved the way for legal positivism in the nineteenth and twentieth centuries. Intellectual historians and legal theorists have generally hailed Vattel as the truly decisive break from the earlier tradition of jurisprudence associated with Gentili and Grotius. The natural law framework of his predecessors relied on universally recognizable principles based in reason, whereas Vattel’s emphasis on consent and voluntarism oriented ‘international law … on its positivist career’ and infused it with ‘wholesome realism.’