The war’s last year began with the Germans in negotiations with Soviet Russia that resulted, in March 1918, in the draconian Treaty of Brest-Litovsk, but only after they had countered Bolshevik stalling tactics by continuing to march eastward, to the detriment of their own plans to withdraw troops for a final offensive in the west. Nevertheless, the final German drive was strong enough to compel unprecedented Allied cooperation, including making Marshal Foch supreme commander. By July the Germans were closer to Paris than at any time since 1914, but American troops gradually assumed a greater role against them, with two-thirds of the 2.1 million to cross the Atlantic deployed to the front by the armistice. British and Imperial troops ultimately mastered combined arms warfare, using artillery, infantry, tanks, and air power to achieve a breakthrough at Amiens in August from which the Germans never recovered. On the Balkan front, a multinational Allied army achieved a breakthrough in September that knocked Bulgaria out of the war, and a month later a breakthrough on the Italian front precipitated the collapse of Austria-Hungary. In the war’s last hundred days, the Allies liberated almost all of France and half of Belgium, prompting Germany to sign the armistice on November 11.