Dutch jurist Hugo Grotius (left) published his seminal work on lawful warfare in 1625. His most influential disciple was Emmerich de Vattel (right), a German-Swiss philospher and jurist. (From left: Michiel Jansz Van Mierevelt; Universitaire de Neuchatel) From left: Michiel Jansz Van Mierevelt; Universitaire de Neuchatel