The Treaty of Westphalia, signed in 1648, established important principles of state sovereignty and non-interference in the internal affairs of sovereign nations. This treaty marked the end of the Thirty Years' War in Europe and laid the groundwork for modern international relations. It recognized the concept of territorial integrity and the idea that each state has the right to govern itself without external intervention. This shift helped to reduce religious wars in Europe by acknowledging the coexistence of Catholic and Protestant states, ultimately leading to a new order in European politics that emphasized diplomacy and state sovereignty.