Westphalian sovereignty is the principle of international law that each nation state has sovereignty over its territory and domestic affairs, to the exclusion of all external powers, on the principle of non-interference in another country's domestic affairs, and that each state (no matter how large or small) is equal in international law. The doctrine is named after the Peace of Westphalia, signed in 1648, which ended the Thirty Years' War, in which the major continental European states – the Holy Roman Empire, Spain, France, Sweden and the Dutch Republic – agreed to respect one another's territorial integrity. As European influence spread across the globe, the Westphalian principles, especially the concept of sovereign states, became central to international law and to the prevailing world order.