Battle of valley of the Marne

The First Battle of the Marne was perhaps the single most important event of the war. Although it was only the first major clash on the Western Front, the First Battle of the Marne was perhaps the single most important event of the war. The defeat of the Germans left the Schlieffen Plan in ruins. In the east, Russian forces had already invaded Germany. Germany was going to have to fight a long war on two fronts.