The Peace of Westphalia, signed in 1648, marked the end of the Thirty Years’ War and is significant for establishing the principles of state sovereignty and non-interference in the internal affairs of states. It recognized the rights of rulers to govern their own territories free from external intervention. This laid the foundation for the modern nation-state system, emphasizing territorial integrity and the importance of negotiated peace, which became central to international law and diplomacy. The peace agreements also encouraged political pluralism in Europe, impacting future international relations and the concept of national sovereignty.