Until about the middle of the seventeenth century, Western European legal writing on the subject of war essentially grew out of a unitary tradition, stemming from the medieval just-war framework, with its roots in natural-law thought. Even when, during the seventeenth century, the voluntary law was brought in, the natural law remained as the base, with the voluntary law as a sort of superstructure. The seventeenth century, however, also witnessed the emergence of two dissident strains of legal thought as challenges to the mainstream tradition. One of them will be labelled the ‘Hobbesian’ school after its principal architect, the English political theorist Thomas Hobbes. At its heart was a view of natural law that was radically at odds with its medieval forebear.