THE FIRST WORLD WAR was a tragic and unnecessary conflict. Unnecessary because the train of events that led to its outbreak might have been broken at any point during the five weeks of crisis that preceded the first clash of arms, had prudence or common goodwill found a voice; tragic because the consequences of the first clash ended the lives of ten million human beings, tortured the emotional lives of millions more, destroyed the benevolent and optimistic culture of the European continent and left, when the guns at last fell silent four years later, a legacy of political rancour and racial hatred so intense that no explanation of the causes of the Second World War can stand without reference to those roots.