How did European leaders discover that a balanced power did not decrease the chances for war?

European leaders discovered that a balance of power did not necessarily reduce the chances for war through a series of conflicts in the 19th and early 20th centuries, including the Franco-Prussian War and World War I. Despite efforts to maintain equilibrium among nations, rivalries and alliances often escalated tensions, leading to miscalculations and military confrontations. The failure of diplomatic measures to resolve disputes highlighted that a stable balance could coexist with aggressive nationalism and militarism. Ultimately, leaders recognized that power dynamics alone could not ensure peace, prompting reconsideration of international relations and the importance of cooperation.