It was Hugo Grotius (a.k.a Huig de Groot) who wrote "De Jure Belli ac Pacis" which for a long time was one of the greatest works on international law,which is why he is often regarded as the father of international law (even if such a title is not entirely deserved; Grotius borrowed many thoughts from the scholastics, the scholastics in turn had read the works of Aristotle).