The Westphalian system, also known as Westphalian sovereignty, is a principle in international law that each state has exclusive sovereignty over its territory. The principle developed in Europe after the Peace of Westphalia in 1648, based on the state theory of Jean Bodin and the natural law teachings of Hugo Grotius. It underlies the modern international system of sovereign states and is enshrined in the United Nations Charter, which states that "nothing ... shall authorize the United Nations to intervene in matters which are essentially within the domestic jurisdiction of any state."[1]
According to the principle, every state, no matter how large or small, has an equal right to sovereignty.[2] Political scientists have traced the concept to the eponymous peace treaties which ended the Thirty Years' War (1618–1648) and Eighty Years' War (1568–1648). The principle of non-interference was then further developed in the 18th century. The Westphalian system reached its peak in the 19th and 20th centuries, but it has faced recent challenges from advocates of humanitarian intervention.[3]
The trajectory traced, in all this, describes a system developing out of the highly centralised and unequal relations that were the mark of the pre-Westphalian stage in international affairs to a Westphalian order in which the sovereign equality of states becomes a defining quality of the system.