January 4, 1913. An old aristocrat rests on his bed, his health fading fast. As Alfred von Schlieffen breathes his last, he reportedly says only this: "Keep the right flank strong." Who was this man, and what did this mean?
When the German Empire came into existence in 1870, it immediately became the greatest power in Europe, but it was vulnerable. Due to the needlessly aggressive foreign policies of Wilhelm II, both France and Russia had signed a mutual defense treaty aimed at Germany. This meant that in any future war, the new Empire would face a war on two fronts and possibly be crushed between them.
Count Alfred von Schlieffen already had a reputation as the most brilliant staff officer in the German Army when he was chosen as the new Chief of the General Staff in 1894. He soon set to work finding a solution to Germany's thorny problem. Schlieffen decided that in the event of war with France and Russia, Germany should go on the defensive, defeat one opponent, then the other. If France declared war first, however...
Schlieffen envisioned bringing 90% of the German Army to the French border and launching it in a massive sweep around Paris, with the overwhelming right flank crushing the French and bringing the war to an end in 60 days. This had to be accomplished quickly because Russia would be on their way to attack, so France would have to be knocked out before the Russians could overwhelm the tiny force left to face them.
There was one problem: the sweep through France required passing through neutral Belgium. Since this would almost certainly bring Britain into the future war, Schlieffen insisted that the attack plan should never be carried out in the event of a two-front war, but was intended for a war against France only.
This plan - known to history as the "Schlieffen Plan" - was ambitious, complex, and immensely detailed. It contained precise instructions for every man in the German Army, railroad timetables, strict schedules, and even went so far as to designate when and where each man would receive his rifle ammunition years in advance.
Schlieffen's reputation, and the magnificence of his grand plan, meant that it soon became Germany's only war plan. The problem was that, due to the plan's complexity, once it was put into action it could not be reversed.
Schlieffen retired in 1906. His successors aa Chief were not his intellectual equals, least of all Helmuth von Moltke the Younger, nephew of Germany's great war leader in the 1860s. Moltke was dull, lethargic and unimaginative, a great name but not a great mind. Despite the changing world order, Moltke adhered to Schlieffen's plan with a slavish stubbornness, even when Schlieffen himself advised that it be changed.
As Schlieffen lay on his deathbed, his plan was already hopelessly out of date. Over his protests, Moltke had married his offensive plan to the defensive one, so that when Russia threatened war all of Germany's armies would rush to France. Even his last plea - "keep the right flank strong" - Moltke would ignore in a moment of panic and indecision, robbing the critical right wing of reinforcements to send to fight Russia when they were needed most in France.
Eighteen months after Schlieffen breathed his last, a legend in his own time, the plan that bore his name launched the Kaiser's army across the Belgian border. A blueprint for victory, its inheritors did not recognize that even the best-laid plans go awry. The German Army fell short of Paris at the Marne. From Schlieffen's failed brainchild came the Western Front of World War I, the great slaughterhouse that heralded the arrival of the twentieth century.
Should be noted that many WWI scholars doubt the existence of a Schlieffen "Plan" at all. There's a lot of debate on this, and Dennis Showalter, Holger Herwig, and Terence Zuber have all covered it. The summary is that Schlieffen had sketches and ideas of general plans, but they probably weren't meant to be taken literally - more as a framework. Though this is debatable.
Book Recommendations: The classic is The Guns of August by Barbara Tuchman (New York: MacMillan, 1962). Tuchman, a popular historian, describes the opening blows of World War I and how they set the world on a trajectory to disaster. Despite her fame, though, old Barb isn't well regarded by many later historians. That being SAID, it's an extremely popular and easy read, and really grasps the sense of Europe plunging into the abyss at the outbreak of World War I. A more scholarly look at the context (and consequences) of Schlieffen's plan is in Robert Citino's EXCELLENT The German Way of War: From the Thirty Years' War to the Third Reich (Lawrence, KS: University Press of Kansas, 2005). Another focused look is in Terence Zuber's Inventing the Schlieffen Plan: German War Planning, 1871–1914 (New York: Oxford University Press, 2002).