For the soldiers, at least on the Western Front, there is no doubt: the war which began in 1914 ended on 11 November 1918, when they no longer had to fear for their lives. But for heads of state, the war ended later, either with the peace treaties or with their implementation. It had begun before mobilization, at the moment of the assassination of Franz-Ferdinand at Sarajevo, or even earlier, with the Balkan wars, or the Franco-German crisis over Agadir. Professional soldiers include the war plans which unfolded on both sides in August 1914. For the French administration, the end of hostilities was fixed by law as 24 October 1919, and emergency regulations lapsed on 15 November. Hence the boundaries of war are not fixed once and for all, because war is not a discrete entity, but something intricately lived, conceptualized, and imagined. It is an actual experience, to which contemporaries gave meaning by thinking about it. The vocabulary acutely discloses this diversity of experiences and meanings. Of course, the words ‘the war of 1914–18’, ‘world war’, or ‘Great War’ do not have precisely the same meaning.

Historical writings are part of this social construction of the historical object. The passage of time induces a kind of sedimentation, and close to a century after these events historians may persuade themselves that they hold a monopoly on this history.