<Li> jus gentium--law of nations </Li> <Li> jus inter gentes--agreements between nations . </Li> <P> The modern study of international law starts in the early 19th century, but its origins go back at least to the 16th century, and Alberico Gentili, Francisco de Vitoria and Hugo Grotius, the "fathers of international law ." Several legal systems developed in Europe, including the codified systems of continental European states and English common law, based on decisions by judges and not by written codes . Other areas developed differing legal systems, with the Chinese legal tradition dating back more than four thousand years, although at the end of the 19th century, there was still no written code for civil proceedings . Some doubt the effectiveness of international law, as they see the implementation of international law as a policy option among others to tackle global dilemmas . They say that international law must be evaluated with other, possibly more effective, international law options . </P> <P> The current order of international law, the equality of sovereignty between nations, was formed through the conclusion of the "Peace of Westphalia" in 1648, the result of a 30 - year war between neoconservative countries and neo-liberal nations . Prior to 1648, on the basis of the purpose of war or the legitimacy of war, it sought to distinguish whether the war was a "just war" or not . This theory of power interruptions can also be found in the writings of the Roman Cicero and the writings of St. Augustine . According to the theory of armistice, the nation that caused unwarranted war could not enjoy the right to obtain or conquer trophies that were legitimate at the time </P>

Who is often regarded as the father of international law