German strategy in the late 19th and early 20th centuries was based on the assumption that, in the event of a war with Russia, Germany would also have to fight France. The result was the Schlieffen Plan, a strategy to knock France out of the war before taking on Russia.
Since losing to Germany in the Franco-Prussian war, the French had been preparing for such an event. They had built sturdy fortifications along their frontier with Germany and had plenty of troops.
Count Alfred von Schlieffen and the German planners who followed him looked for a way to avoid those defenses. The result was a plan to invade France through Belgium. The Germans would quickly overcome the weaker Belgians, swing around the flank of the French armies, surround them and force them to surrender.
