They did. The entire German war goal was to not only defeat France, but do it quickly, in 6 weeks or so. They did this by invading neutral Belgium and Luxembourg to encircle the French army concentrated at Alsace-Lorraine. This was also much easier territory to navigate through, so the German army could not only move quickly, but safely as there were no major river crossings or hilly terrain. They came very close to Paris (60 miles or so?) but were eventually halted at the first Battle of the Marne by French-Anglo forces. Until then, Germany made huge gains in territory in the north with their large force. The Guns of August by Barbara Tuchman is a great book about the buildup to and first month of the war. Coming up on the centennial I find myself reading a lot lately about the war.