The Peace of Westphalia consists of a series of peace treaties that ended the Thirty Years' War in the Holy Roman Empire and the Eighty Years' War between Spain and the Dutch Republic. This event is considered the birth of the modern international system of sovereign states. It established the principle of 'cuius regio, eius religio' (whose realm, his religion), allowing princes to choose the religion of their own states. More importantly, it introduced the concept of 'Westphalian Sovereignty,' which dictates that states should not interfere in the internal affairs of other sovereign states. This became the foundation for modern international law and diplomacy. The treaty also recognized the independence of Switzerland and the Netherlands, and shifted the balance of power in Europe toward France and away from the Habsburgs.