The Peace of Westphalia, concluded in 1648, established the principle of state sovereignty and marked the end of the Thirty Years' War in Europe. This series of treaties recognized the right of states to govern their territory without external interference, laying the groundwork for modern international relations. The Westphalian model emphasized legal equality between states and the idea of non-intervention, fundamentally altering how nations interacted. This shift paved the way for the development of the nation-state system, influencing international diplomacy and conflict resolution for centuries to come.