First Battle of the Marne

In early September 1914, German armies advancing through Belgium and northern France approached Paris but altered their planned wheel around the city, exposing a gap between major formations. French and British armies counterattacked along the Marne from September 6, forcing the Germans to retreat toward the Aisne. Paris taxis did transport several thousand French reservists to the front, but their military effect was modest compared with their symbolic importance. The battle stopped the German advance on Paris and helped end hopes for a quick decision in the west; trench warfare soon solidified across much of the front.

The German retreat was ordered in person by a staff officer, Lieutenant Colonel Hentsch, sent forward from headquarters with authority that has been disputed ever since, and German writers spent the interwar years arguing about whether he exceeded it and whether Moltke had lost his nerve. The French called it a miracle almost immediately, a framing the Third Republic found useful and which has made the battle harder rather than easier to study. The larger argument concerns the Schlieffen Plan itself, which Terence Zuber challenged in the late 1990s as a postwar construction rather than a plan the army was executing, a thesis that remains contested and that changed the terms of the debate regardless of who is right. What is not disputed is what the outcome produced, since the failure to decide the war quickly left both sides with a front they then spent four years attacking.