The Guns of August — Barbara Tuchman

Tuchman's account of the first month of the First World War — the mobilisations, the invasions, the collapse of pre-war assumptions — remains, sixty years after publication, the most readable account of how the war began and how it immediately escaped the control of the men who had planned it. The Schlieffen Plan, the German invasion of Belgium, the first Battle of the Marne: Tuchman shows how each decision constrained the next until the war that nobody had quite intended was fully under way.