Which battle marked the Germans first major defeat during World War I?

The Battle of the Marne was a World War I battle fought from 6–12 September 1914. It resulted in an Allied victory against the German armies in the west. The battle was the culmination of the German advance into France and pursuit of the Allied armies which followed the Battle of the Frontiers in August and had reached the eastern outskirts of Paris. A counter-attack by six French armies and the British Expeditionary Force (BEF) along the Marne River forced the Imperial German Army to retreat northwest, leading to the First Battle of the Aisne and the Race to the Sea. The battle was a victory for the Allied Powers but led to four years of trench warfare stalemate on the Western Front.

The battle of the Marne was a major turning point of World War I. By the end of August 1914, the whole Allied army on the Western Front had been forced into a general retreat back towards Paris. Meanwhile, the two main German armies continued through France. It seemed that Paris would be taken as both the French and the British fell back towards the Marne River. The war became a stalemate when the Allied Powers won the Battle of the Marne. It was the first major clash on the Western Front and one of the most important events in the war. The German retreat left the Schlieffen Plan in ruins and Germany had no hope of a quick victory in France. Its army was left to fight a long war on two fronts.