Law of nations

Public international law concerns the structure and conduct of sovereign states; analogous entities, such as the Holy See; and intergovernmental organizations. To a lesser degree, international law also may affect multinational corporations and individuals, an impact increasingly evolving beyond domestic legal interpretation and enforcement. Public international law has increased in use and importance vastly over the twentieth century, due to the increase in global trade, environmental deterioration on a worldwide scale, awareness of human rights violations, rapid and vast increases in international transportation and a boom in global communications.

The field of study combines two main branches: the law of nations (jus gentium) and international agreements and conventions (jus inter gentes).

The Italian jurist Sir Alberico Gentili was the first to write on public international law. It is usually distinguished from "private international law", which concerns the resolution of conflict of laws. In its most general sense, international law "consists of rules and principles of general application dealing with the conduct of states and of intergovernmental organizations and with their relations inter se, as well as with some of their relations with persons, whether natural or juridical."

Beginning with the Peace of Westphalia in 1648, the 17th, 18th and 19th centuries saw the growth of the concept of the sovereign "nation-state", which consisted of a nation controlled by a centralized system of government. The concept of nationalism became increasingly important as people began to see themselves as citizens of a particular nation with a distinct national identity. Until the mid-19th century, relations between nation-states were dictated by treaty, agreements to behave in a certain way towards another state, unenforceable except by force, and not binding except as matters of honor and faithfulness. But treaties alone became increasingly toothless and wars became increasingly destructive, most markedly towards civilians, and civilized peoples decried their horrors, leading to calls for regulation of the acts of states, especially in times of war.

...
Wikipedia