The Schlieffen Plan was the name given to the German military strategy for defeating France and Russia in World War I. It was developed by Count Alfred von Schlieffen, who was the Chief of the German General Staff from 1891 to 1906. The plan called for a massive invasion of France through Belgium and Luxembourg, with the aim of defeating the French army in a decisive battle within six weeks. If this could be achieved, Germany would then be free to turn its attention to the Eastern Front and defeat Russia.
The Schlieffen Plan was based on a number of factors, including the belief that France and Russia would not be able to mobilize their armies quickly enough to stop the German advance. It also assumed that the French army would try to defend its border with Germany, rather than retreating to the south.
In the event, the Schlieffen Plan did not work as expected. The French were able to retreat in good order, and the German army was unable to achieve a decisive victory. The British Expeditionary Force also arrived in France and contributed to the French defense. As a result, Germany was forced to fight a two-front war, which eventually led to its defeat.