The First World War was launched in the belief that force could be an effective instrument of policy. Underlying the decisions of July and August 1914 was a hard core of calculation, based on the advice to governments that the fighting would be fierce but short, and that its political and economic repercussions could be contained. In addition, because the two sides were closer to military equivalence than in previous crises, both could believe that they had a reasonable prospect of victory. But such equivalence, given the weapons technology of the day, might also deny either coalition a speedy, surgical triumph. And it is from the prolongation of the war as well as its inception – from its not being over by Christmas – that its historical importance derives. Among the consequences were eight million dead, and the dislocation of the Western economic system. Without the war it is unlikely that either Lenin, or Mussolini, or even Hitler, would have come to office. As far as such things can be said with certainty, the First World War was a precondition of the Second. A four-month rather than a four-year conflagration would have had other, now unknowable, consequences. It would not, presumably, have had these.