As you likely know, The Schlieffen Plan was the German army’s plan for war against France and Russia. It was inspired by the Carthaginian envelopment of the Romans at the Battle of Cannae in 216 BC during the Second Punic War. Hannibal's troops, though fewer in numbers, used speed to outflank and then surround the Romans, who suffered one of their worst defeats every. The Germans believed they could use those tactics to defeat France, their traditional enemy. The German Chief of Staff Alfred von Schlieffen was the plans architect and in 1903 drafted the plan at the request of Kaiser Wilhelm II. Schlieffen faced a serious problem. Germany was not threatened by one enemy; rather, it had France in the west and Russia in the east. The mighty empires were allies and Germany would have to quickly defeat one while holding off the other. Key to success would be speed. To accelerate the transfer of troops between future fronts, Schlieffen advised the Kaiser to build efficient railroads to move troops quickly between the fronts.

The Germans believed Russia would be slow to act, and minimal forces could hold them in check. The problem with France was the approach of the attack. The most viable route was through Belgium but this would violate Belgian neutrality and trigger an old treaty of protection between Belgium and England dating back to the Napoleonic era. The Germans believed they could advance rapidly before England could act. The timeline for victory was six weeks.

In 1906, Helmuth von Moltke the Younger succeeded Schlieffen as Chief of the German General Staff. He had doubts about the possibility of a German victory in a great European war. He worried that France might use tactical withdrawals and not offer the grand battle Germany wanted, thereby leading to a conflict of attrition. As time went by, Moltke tweaked the plan. Deciding to honor Dutch neutrality, the German armies would have to squeeze the 600,000 men through a gap 12 miles wide, which made it vital that the Belgian railways were captured quickly and intact. In 1908, the General Staff devised a plan to take the Fortified Position of Liège and its railway junction by the 11th day of the attack. Later amendments accelerated the time to the 5th day, which meant that the attacking forces would need to get moving only hours after the that attack was launched. The Germans intended to intimidate the Belgian people using a scorched earth policy Instead of immediately surrendering, Belgium settled in for a long fight, delaying the German advance.

In 1914, Germans advanced through Belgium and northern France against the Belgian, British and French armies and approximately 20 miles from Paris. They failed to envelop the Allied armies and force a decisive battle on them. The Germans outran their supplies, and the French rallied to stop the German advance, with a counter-offensive at the First Battle of the Marne, assisted by the British.

The controversy emerged following the war. One school of thought held that German General Staff had used the wrong war plan, rather than failed adequately to follow the right one. The Germans should have defended in the west and attacked in the east. This was countered by those who believed the war could only have been won with the defeat of France and Britain.

Sources: Foley, R. T. (2006) [2003]. Alfred von Schlieffen's Military Writings. London: Frank Cass. ISBN 0-71464-999-6.

https://www.mtholyoke.edu/~jedzi20h/classweb/The%20Schlieffen%20Plan.html