The emergence of theEuropean Union has been one of the defining events of the twentieth century. It has changed the political, economic, and social landscapes of WesternEuropean, changed the balance of power in the world by helpingEurope reassert themselves on the world stage, and helped to bring the longest uninterrupted spell of peace inEurope recorded history. Until the beginning of the twentieth century,Europe was a continent of competing powers that repeatedly fought with each other on their own soil and took their mutual hostilities to other continents in their competition to build colonial empires. The tragic costs of nationalism were finally confirmed by two world wars, fought largely onEurope and leaving theEurope powers devastated and draineD、IfEurope had not learned of the barbarism and futility of war in the trenches of northern France andBelgium in 1914~1918, the horrors of the period 1939～1945 finally brought home the need to cooperate and to build the kind of society that would eliminate the seeds of conflict.