Schlieffen Plan vs. Plan XVIIGermany didn't want to fight both Russia in the east and France in the west, so they enacted their long-standing Schlieffen Plan. The Schlieffen Plan was created by Alfred Graf von Schlieffen, who was the chief of the German general staff from 1891 to 1905.Schlieffen believed that it would take about six weeks for Russia to mobilize their troops and supplies. So, if Germany placed a nominal number of soldiers in the east, the majority of Germany's soldiers and supplies could be used for a quick attack in the west.
Since Germany was facing this exact scenario of a two-front war at the beginning of World War I, Germany decided to enact the Schlieffen Plan. While Russia continued to mobilize, Germany decided to attack France by going through neutral Belgium. Since Britain had a treaty with Belgium, the attack on Belgium officially brought Britain into the war.
While Germany was enacting its Schlieffen Plan, the French enacted their own prepared plan, called Plan XVII. This plan was created in 1913 and called for quick mobilization in response to a German attack through Belgium.
As German troops moved south into France and the French and British troops moved north to meet them, the massive armies met each other in a stalemate. By September 1914, neither side could force the other to move, so each side began to dig trenches. For the next four years, the troops would fight from these trenches.