When World War I began, Germany implemented the Schlieffen Plan—a strategy for a swift advance through Belgium to Paris, with the goal of encircling and capturing the French capital from the west. At first, the plan unfolded successfully, pushing France into a critical position. However, as the campaign progressed, the German army found itself without enough troops to complete the encirclement of Paris. German high command then altered their strategy, shortening their offensive route, abandoning the planned bypass of Paris, and redirecting forces eastward toward the Marne River.
France and Britain responded decisively by concentrating forces in this vulnerable sector, assembling an Allied force nearly twice the size of the advancing German armies. Their powerful counterattack forced the Germans to stretch their lines thin while attempting to maneuver along the front. As gaps appeared in the German formations, French and British units quickly exploited these weaknesses by advancing into the openings.
This pressure ultimately forced the Germans to retreat, marking the complete collapse of the Schlieffen Plan, which had been designed for a rapid victory on the Western Front. This unexpected Allied triumph later became known as the ‘Miracle on the Marne’.