Which treaty of 1648 ended the Thirty Years' War?

The Peace of Westphalia, which is usually credited with inventing the modern state system - the principle that a state has exclusive authority within its own borders and that outside powers do not intervene in its internal affairs, particularly its religion.

The war it ended was the most destructive in European history before the twentieth century. Central Europe lost perhaps a third of its population in some regions - to fighting, famine and disease, with mercenary armies living off the country they marched through. Whole districts were depopulated and did not recover for generations.

Historians have spent recent decades arguing that the Westphalian system is largely a retrospective construction - the treaties themselves are practical documents about territory and religious rights, they do not state a doctrine of sovereignty, and the term Westphalian sovereignty appears to date from the twentieth century. The idea got its name because international relations theorists needed a founding moment, and 1648 was available.