The central tenet of the Treaty of Westphalia, signed in 1648, was the principle of state sovereignty, which established the modern nation-state system. This treaty ended the Thirty Years' War in Europe and recognized the rights of individual states to govern themselves without external interference. It marked a significant shift from a religiously polarized order dominated by the Catholic Church towards a system where political boundaries were respected and states were seen as sovereign entities. The treaty laid the groundwork for contemporary international law and diplomacy while promoting the idea that states could coexist despite differing religious beliefs.