Russian plans for the start of the war called for simultaneous invasions of Austrian Galicia and East Prussia. Although Russia's initial advance into Galicia was largely successful, it was driven back from East Prussia by Hindenburg and Ludendorff at the battles of Tannenberg and the Masurian Lakes in August and September 1914. Russia's less developed industrial base and ineffective military leadership were instrumental in the events that unfolded. By the spring of 1915, the Russians had retreated from Galicia, and, in May, the Central Powers achieved a remarkable breakthrough on Poland's southern frontiers with their Gorlice–Tarnów Offensive. On 5August, they captured Warsaw and forced the Russians to withdraw from Poland.