 Complete the following phrase:  At the outbreak of war in August 1914, Fochs XX Corps participated in the brief invasion of Germany before retreating in the face of a German counter-attack and successfully blocking the Germans short of Nancy. Ordered west to defend Paris, Fochs prestige soared as a result of the victory at the Marne, for which he was widely credited as a chief protagonist while commanding the French Ninth Army. He was then promoted again to Assistant Commander-in-Chief for the Northern Zone, a role which evolved into command of Army Group North, and in which role he was required to cooperate with the British forces at 