Gorlice-Tarnow Breakthrough

May 1915: To help the Austro-Hungarians, a new German army is formed under the capable von Mackensen, and placed in the line east of Crackow. He attacks and completely pierces the Russian lines. A Russian retreat ensues that enables the Central Powers forces to recapture most of Galicia. After being pressured by the Kaiser, von Falkenhayn gave into the insistence of Hindenburg and Ludendorff, resulting in a widening of the offensive.
The Central Powers offensive wound down as they struggled to supply troops hundreds of miles past the supply heads. The offensive has saved Austria-Hungary from immediate peril, but it does not knock Russia out of the war. And instead of enabling von Falkenhayn to focus on the west, most of the newly created German forces are fed into the increasing vastness of the eastern front.