During this first phase of the fighting in 1914, the war was a mobile one, much as prewar planners had anticipated. Field armies confronted one another, either seeking to break through to victory, or, more frequently, to slide around the enemy's flank to gain a decisive advantage. The German army, invading France via Belgium, marched and fought over a distance of 300 miles. Russian troops thrust as much as 75 miles into the German province of East Prussia, while other Russian armies cut deeply into Austrian Galicia. But none of these great sweeps, impressive on the map and conducted in accordance with prewar hopes, brought decisive victory. The German war plan—known in honor of its creator as the Schlieffen plan—offered the clearest set of goals. In its key feature, it called for German forces to drive through Belgium (a neutral country), thus avoiding the massive French fortifications facing the German border. Moving southward and southwestward, they would push, crowd, and then annihilate the French army against its own eastern border, crushing France's ability to continue fighting in one great offensive campaign. Victory in the west would come in less than two months. German forces then were to move eastward for a longer but no less decisive offensive against the Russians. The failure of the Schlieffen plan built the foundation for the prolonged war that followed in western Europe. The fighting there has offered the most vivid, horrible images of what World War I was like. The German offensive seemed at first to meet with striking success. The Belgian army and Belgian fortifications offered more resistance than German planners had foreseen, but the march went generally according to the timetable. France's commanders were caught off guard, since they never anticipated such a massive German concentration in the north. And they were off to conduct their own offensive—with objectives far less clear and less ambhious than those of the Schlieffen plan—against the German border regions further south. As German forces advanced westward into Belgium and swung southward toward the undefended Franco-Belgian border, the five divisions of the British Expeditionary Force took their place along the left (western) flank of the French. They too were soon pushed along in the overall Allied retreat. But the Schlieffen plan did not work. The French and British both conducted a fighting retreat, impeding the German advance while keeping their own forces intact. German efforts to sweep around to the western flank of the enemy never succeeded. Their field armies—advancing each day over vast territories, encountering spirited enemy resistance, and uncoordinated by higher authority—tended to pull away from one another during the advance; this opened dangerous gaps into which the French or possibly the British could counterattack. In a momentous but almost inevitable decision, the generals in the field modified their orders. They would shorten their line of advance, pursuing the French forces while remaining east of the French capital—and powerful fortress—of Paris. Meanwhile, German troops were exhausted by weeks of marching and fighting. Of course, the British and French had to cover the same ground, but the Germans were pulling perilously far from their supply bases. As German generals, in particular the overall commander von Moltke, grew first uncertain, then pessimistic, and finally panicky, the key figure on the Allied side, France's General Joseph Joffre, remained unruffled and even confident. In early September the tide turned. The French and British counterattacked northward against the overextended Germans along the Mame River. Meanwhile, a newly created French army based in Paris struck the Germans from the west. By September 9, the Germans were compelled to pull back. The Schlieffen plan had failed, and any hopes of a quick German victory in the west evaporated. But they pulled back only to strong defensive positions, such as those along the Aisne River, that soon expanded to become a steady line of trenches stretching from the Swiss border to the English Channel. If the Germans had failed to win a decisive victory, they ended up occupying most of Belgium and large areas of northeastern France. The war on the western front was to center on efforts to push them from the consolation prize they had taken in the late summer of 1914.