The Battle of Tannenberg was a WW1 military engagement that took place on the Eastern Front during the Russian invasion of East Prussia. It was fought between the German 8th Army, under Paul von Hindenburg, and the Russian 2nd Army, led by Alexander Samsonov, from August 27 to August 30, 1914. The result was a German victory.
Summary
On August 17, the Russian forces began the invasion of East Prussia from south and east, with two armies. To stop the enemy advance, the German emperor, William II, sent the 8th Army, led by General Maximilian von Prittwitz. However, after the Germans had been defeated by the Russians at the Battle of Gumbinnen, von Prittwitz was replaced by Paul von Hindenburg, who immediately ordered the 8th Army to move forwards.
Being on the offensive, the Germans managed to surround the Russian forces at Tannenberg, a village in East Prussia (today northern Poland). Thus, the Russian 2nd Army was encircled and defeated. Samsonov committed suicide at the end of the battle. This German victory basically stabilized and secured the Eastern Front. The reason for the German victory was due to fact that the Russain 1st Army’s commander failed to forestall the German advance on Tannenberg.
Meanwhile, on the Western Front, the Imperial German Army, under von Moltke, was about to defeat the French and Belgian forces at the Battle of the Frontiers.
Below, Battle of Tannenberg military map, which shows the opposing forces positions on August 27, 1914.