The European treaty that established the principle of balance of power was the Treaty of Westphalia, signed in 1648. This treaty ended the Thirty Years' War in Europe and consisted of multiple agreements between various states, including France, Spain, and the Holy Roman Empire. The Treaty of Westphalia is significant because it marked the beginning of a new political order in Europe, emphasizing state sovereignty and mutual recognition among nations. It established a framework for international diplomacy and the concept of balancing power among states to prevent any one nation from becoming too dominant, a principle that remains influential in international relations today.