Seen from Berlin, Germany's leaders could point to the success of halting enemy offensives everywhere. But there was the even greater sadsfaction of massive advances. The conquest of Serbia was one example that paled, however, compared to the German push into the Russian Empire. Germany's spectacular success against Russia came largely out of necessity. In the winter of 1914-1915, Russian forces seemed poised to cut through the last line of mountain defenses and to plunge into the heartland of the Austro-Hungarian Empire. To maintain the security of Germany's most crucial ally, General Erich von Falkenhayn, Moltke's successor, sanctioned a major offensive on the eastern front. Striking northward through the Carpathian Mountains, a combined German and Austrian force under General August von Mackensen punched through Russian defenses at Gorlice-Tamow and thrust into the enemy's rear. The desperate Russians were blown aside by one overwhelming artillery barrage after another. Mackensen's artillery at Gorlice outnumbered the Russians in light artillery, 1,272 pieces to 675. And the Russians had no weapons to match the Germans' 334 pieces of heavy artillery. In the face of unlimited supplies of shells on the German side, Russian soldiers had permission to fire only two howitzer shells per day. Starting in early July, Hindenburg and Ludendorff drove southward from their bastion in East Prussia to add to the Russians' calamity. Facing certain annihilation, desperate Russian commanders withdrew from vast areas that had constituted the western bastion of the Russian Empire. By the time the German offensives merged in late August, Russia had lost all of its Polish territories and German armies were penetrating the Russian-speaking core of the tsar's possessions. Russian losses, unlike those of the British and the French on the western front, included vast numbers of troops taken prisoner. But the most important result of the 1915 disaster was a Russian military system shaken to its core. Following this triumph, soon augmented by the advance into Serbia, which the tireless Mackensen also directed, Germany could now claim to be unbeatable on land. Its forces were within striking range of both Paris and St. Petersburg; it had established a direct land link with its Turkish ally; its defenses had proven impenetrable to French, British, and Russian attacks. In reality, however, a German victory was far from assured. Both alliances continued to mobilize greater resources, as more countries were being drawn into the conflict, but for both sides the conclusive defeat of the enemy remained out of reach. The tactical advantages enjoyed by the defensive side barred the way against decisive offensives on many fronts. Moreover, seemingly decisive offensives brought military advantages but nothing more. Nations committed to victory would not give up, even after suffering dramatic losses. Even Germany's deep penetration into Russian territory did not suffice to bring an end to the war on the eastern front. With the will to win undiminished on all sides, most of Europe's population was condemned to a continuing conflict.