Once thought to be "the war to end all wars", World War I was fought from July 28, 1914 to November 11, 1918. As the conflict's main players arranged themselves into the Allied Powers (the U.K., the U.S., France, the Russian Empire, Italy, Japan, Portugal, Greece, Serbia, and Montenegro) and the Central Powers (the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, and Bulgaria), Germany began an aggressive two-pronged attack. The Schlieffen Plan—so named for the strategic man behind it, German Field Marshal Alfred von Schlieffen—would see Germany invading France in the west and then rapidly confronting Russia in the east.
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The Schlieffen Plan was expected to not only bring the Central Powers victory, but an exceptionally quick one. This offensive led to significant defeats of the Franco-British forces during the Battle of Charleroi and the Battle of Mons. These Allied forces began what was called The Great Retreat—a withdrawal to the River Marne. Along the way, the French Fifth Army attempted a counter-offensive at the First Battle of Guise, but their failure saw a continued retreat.
It wasn't until the First Battle of the Marne that the tides of war began to change.
Leading Up to the Battle
German General Helmuth von Moltke issued a General Directive on September 2, 1914 that would set the stage for the fateful First Battle of the Marne, which took place from September 6 to September 12. Rather than having German forces directly infiltrate Paris, the city was to now be bypassed. Instead, the Germans were ordered to pin down the French forces between Paris and Verdun.
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The plan was for the German 2nd Army to act as the primary striking force, while the 1st Army followed behind to guard the flank. But as communication between the two German forces disintegrated, so too did their iron grip on victory. The commander of the 1st Army, Alexander von Kluck, disregarded Moltke's change in orders, maintaining his path to the southeast in anticipation of going through with an offensive strike rather than reinforcing the west. When Kluck communicated his own plans to Moltke two days later on September 4, Moltke proceeded to ignore Kluck in return.
Meanwhile, French Commander-in-Chief Joseph Joffre made the decision to remove General Charles Lanrezac as commander of the Fifth Army. He replaced him with I Corps Commander Louis Franchet d'Espèrey, who called for a surprise counterattack against the German forces.
French Forces Gain the Advantage
On the western flank, Joffre issued orders on September 4 for the 6th Army to attack eastward towards Château Thierry. The British Expeditionary Force (BEF) continued toward Montmirail, while the 5th Army launched a northward attack with protection from a right flank of the 9th Army.
September 5 saw the Battle of Ourcq between the Sixth Army and the German IV Reserve Corps. While the IV Reserve Corps managed to push the 6th Army back, Kluck heard news of the attack and redirected his troops west. However, poor communication in this maneuver caused a quick-widening gap to form within the German forces—a gap which Allied aerial forces quickly spotted. It was an opportunity they were prepared to seize.
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The Allies sent the BEF and the 5th Army to exploit the weak point between the German armies. September 6th saw the 5th Army pinning down the 2nd Army in the Battle of the Two Morins. While the BEF moved at an infuriatingly slow pace for General d'Espèrey, they did manage to capture bridges over the Marne to establish a bridgehead. And by September 8, the 5th Army's arrival in Petit Morin forced the right flank of the 2nd Army to withdraw.
On the 9th, the 5th Army crossed the Marne river again, this time headed in the direction of the Germans. The Germans had hoped to crush the 6th Army, but they were disheartened to see that it had been reinforced. This brilliant move added 10,000 French reserve infantry soldiers from Paris—3,000 of which had been 7th Division soldiers brought to the frontlines by Parisian taxicabs requisitioned by General Gallieni.
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All the while, no reports were exchanged between Moltke and Kluck or Bülow. As the Sixth Army held their ground, the 5th Army launched a surprise offensive against the 2nd Army. The 1st and 2nd Armies initiated a hasty retreat. When Moltke finally heard news of the danger, he spiraled into a nervous breakdown, leaving his subordinates to coordinate the retreat.
More than two million soldiers participated in the First Battle of the Marne. Casualties for the French and Germans came out to around 250,000 apiece, with 80,000 Frenchmen thought to have been killed and about 67,000 Germans killed. The British saw 13,000 casualties, including 1,700 deaths.
While historians agree across the board that the First Battle of Marne was a strategic victory for the Allies, the extent of that victory is hotly debated. It's true that through this confrontation the French not only saved Paris from falling into the hands of the Central Powers, but kept themselves in the war with a fighting chance. However, Germany continued to occupy a significant portion of Northern France and Belgium.
One thing is certain about this important conflict: Its surprising outcome set both sides up for a war that was longer and more disruptive than they had bargained for. Far from a quick and decisive end to the conflict, the Battle of the Marne would be followed by four more years of excruciating attrition warfare that would cost millions of lives.