Was the German defeat on the Western Front caused by the failure of the Schlieffen Plan?

After German foreign policy had caused the country to have hostile countries on either side - France and Russia - Germany needed a plan to win a war on two fronts. This plan was devised in the early twentieth century by Count Alfred von Schlieffen and then tinkered with fairly extensively by the younger Moltke right up until 1914. It is known as the Schlieffen Plan. The plan's idea was to have a lightning invasion of …

…in 1916 before the Americans had come, before Germany's main allies, Turkey and Austria, were imploding, such an offensive could have happened then and won Germany the war in the West. The fact that the Schlieffen Plan failed did not mean it was no longer possible for Germany to win in the west: as I explained above, there were other possibilities for German success in the war. It did, however, make it a whole lot harder.