The 15th century saw a confluence of factors that contributed to accelerating the development of international law within its current framework. The influx of Greek scholars from the collapsing Byzantine Empire, as well as the introduction of the printing machine, stimulated the development of science, humanism and notions of individual rights. The strengthening of navigation and exploration by Europeans has invited scientists to develop a conceptual framework for relations with different peoples and cultures. The creation of centralized states, such as Spain and France, brought more prosperity, ambition and trade, which in turn required increasingly demanding rules and rules. During the European Middle Ages, international law focused on the purpose and legitimacy of war to determine what constituted a “just war”. For example, the theory of armistice maintained the nation that caused unjustified war, could not enjoy the right to receive or conquer trophies that were legitimate at that time.  The notion of Greco-Roman natural law was combined with religious principles by the Jewish philosopher Moses Maimonides (1135-1204) and the Christian theologian Thomas von Aquin (1225-1274) with religious principles to create the new discipline of the “law of nations” which, unlike his Roman predecessor of the same name, applies natural law to relations between states. In Islam, a similar framework was developed, in which the law of nations was partly inferred from the principles and rules established in treaties with non-Muslims.  Spain, whose world empire in the 16th and 17th centuries spurred a golden age of economic and intellectual development, made important contributions to international law. Francisco de Vitoria (1486-1546), who examined Spain`s treatment of indigenous peoples, invoked the law of nations as the foundation of their innate dignity and rights and expressed an early version of sovereign equality between peoples. Francisco Suarez (1548-1617) stressed that international law was based on natural law. The concept of sovereignty was disseminated throughout the world by European powers that had built colonies and spheres of influence on virtually all societies.
Positivism reached its peak at the end of the 19th century and its influence began to weaken after the unprecedented bloodbath of the First World War, which inspired the creation of international organizations such as the League of Nations, founded in 1919, to ensure peace and security. International law has begun to integrate more natural concepts such as self-determination and human rights. The Second World War accelerated this development and led to the creation of the United Nations, whose Charter enshrined principles such as non-aggressiveness, non-interference and collective security. It was followed by a stronger international legal order, supported by institutions such as the International Court of Justice and the UN Security Council, as well as multilateral agreements such as the Genocide Convention. The Commission on International Law (ILC) was established in 1947 to assist in the development, codification and strengthening of international law. These include efforts such as the Proliferation Security Initiative (PSI) and the G7 Global Partnership Against the Proliferation of Weapons of Mass Destruction. Although the PSI has a “declaration of prohibition principles” and the G7 Global Partnership includes several statements by G7 heads of state and government, it also does not have a legally binding document that sets specific obligations and is signed or ratified by member states.