At the outbreak of war in August 1914, Foch's 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, Foch's 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 Ypres and the Somme. At the end of 1916, partly owing to the disappointing results of the latter offensive and partly owing to wartime political rivalries, Foch was transferred to Italy. Foch was appointed "Commander-in-Chief of the Allied Armies" on 26 March 1918 following being the Commander-in-Chief of Western Front with the title Généralissime in 1918. He played a decisive role in halting a renewed German advance on Paris in the Second Battle of the Marne, after which he was promoted to Marshal of France. Addington says, "to a large extent the final Allied strategy which won the war on land in Western Europe in 1918 was Foch's alone."