Entering World War I, Germany knew that it could not wage war for an extended period on two fronts. Therefore, it became necessary for them to attempt to destroy one opponent quickly and decisively allowing them to concentrate all their forces on the other. Only a rapid offensive strategy would fulfill this objective. The plan which they devised was designed by Count Alfred von Schlieffen, Chief of the German General Staff from 1891-1906.
The Franco-Russian Alliance made it clear that Germany would have to face both French and Russian forces if they were ever to get in a war with either one. Consequently, the Germans believed that they would destroy France before Russia had time to mobilized. Germany estimated that it would take both themselves and France two weeks to mobilized. On the other hand, the Germans believed that it would take Russia six weeks to muster an offensive counter attack against them. The reason the Germans believed this is because of the closer proximity of France and the technological inferiority of Russia.
As early as 1899, Schlieffen had developed a plan of attack against France. Schlieffen realized that Germany could not attack straight across their border due to the fortresses which France had built along Alsace and Lorraine after 1870. Therefore, at the heart of Schlieffen plan was the idea that Germany would have to attack France by first going through Belgium. Because Belgium had been neutral since 1839, it was assumed to be an easy target which would provide the Germans with quick access into France. Additionally, Schlieffen predicted that France would eventually attack through Belgium, so Germany might as well do so first.
At the beginning, Schlieffen planned only to attack through a small portion of Belgium. Eventually, however, he was persuaded by German nationalists to expand his plans to attack through all of Belgium. The first wave of the attack called for a great wheeling movement through Belgium. A wheeling movement would allow the Germans to circle around behind Paris and capture the French armies at the Gura Mountains and the Swiss frontier. Schlieffen was inspired to do this by Hannibal's defeat of the Romans at Cannae. Schlieffen allocated six weeks and 7/8 of Germany's forces to destroy France while 1/8 held the Eastern Front against Russia.
Although Schlieffen died in 1912, Germany still used his plan when the war broke in 1914. The plan ultimately failed because of unexpected Belgian resistance which slowed the German offensive enough for the French to rally and defeat them at the Battle of Marne. After the Battle of Marne both sides settled into trench warfare for the duration of the War.
Harmann, David G. The Arming of Europe and the Making of the First World War. Princeton University Press, 1996.
Fleming, D.F. The Origins and Legacies of World War I. Garden City, New York: Doubleday and Company, Inc., 1968.
Tuchman, Barbara W. The Guns of August. New York: MacMillan Company, 1962.