According to Holmes, from Swansea University, the Schlieffen plant was intended to knock France out of the war in short order so that the German army could focus on the war with Russia. They knew that war with Russia was an inevitability, and thusly planned to knock out the threat of France as quickly as possible, preferably before they could mobilize their forces, to ensure as much military force as was possible for the war in the east.

This plan was complicated by the British entry to the war due to their treaty with Belgium dating from 1839. The Germans assumed that Britain would not go to war for a "scrap of paper". Their miscalculation led to the stalling of the Schlieffen plan at the Battle of the Marne, thus propelling Germany into a protracted two-front war.

^1 Holmes, T. M. (2014). Absolute Numbers: The Schlieffen Plan as a Critique of German Strategy in 1914. War In History, 21(2), 193-213. doi:10.1177/0968344513505499

^2 Treaty of London, 1839: The Complete Text. http://www.scottmanning.com/content/treaty-of-london-1839/