In the first months of WWI, both the Eastern and Western Fronts were very mobile. In the west, Germany advanced into Belgium and France outflanking their enemy and occupying valuable territory. In the east, Russian, German, and Austrian armies clashed, the use of railways enabling the easy movement and concentration of forces. The initial Russian offensives in the east culminated in the Battle of Tannenberg, which ended on August 30th, 1914.
Before the war, both sides made plans for each of the probable scenarios. The German Schlieffen plan called for an invasion of France through Belgium in order to quickly knock the country out of the war. The German armies would then move east to defeat the Russians, who would take longer to mobilize due to their poor infrastructure. The Franco-Russian plan included a French invasion of Alsace-Lorraine and a Russian invasion of East Prussia. The Germans activated their plan first and swept into Belgium in early August. In the east, the Russians crossed into German territory on August 17th. This was earlier than the Germans had expected, and so the Eighth Army was caught outnumbered against the Russian 1st and 2nd Armies. Following a few initial engagements in which the Germans had some success but were unable to throw the Russians back, Generals Paul von Hindenburg and Erich Luddendorf were sent to take charge of the army; they arrived on August 23rd. The Russian First Army was concentrated in the North against the City of Konigsberg, while the Second Army was south and west. The German commanders decided to concentrate their forces against the Second Army, and to that end used rail lines to quickly move their troops to threaten the Russian left flank. The Second Army continued to advance into German territory with the intent of cutting off East Prussia. Russian General Samsonov only detected the German build up on his left on the 26th. He sent reinforcements, but they would not arrive for several days, slowed down by poor roads and inefficient transportation. Initial German attacks on the 26th achieved little, but on the 27th they captured the critical town of Usdau and pushed the Russian right flank back. In the center the Russians continued to advance, but Samsonov began to realize that his army was in danger of being surrounded. The First Army sent a contingent south to aid the Second Army, but it would not arrive in time to take part in the battle. By the 28th the Russian center was out of food and ammunition and so could not maintain its attacks and the left and right were in retreat. The Germans formed a line between the towns of Neidenberg and Willenberg, cutting the Russians off from behind and surrounding them. On the 29th the Germans began liquidating the pocket they created. The few Russians on the outside failed to break the German lines and those on the inside were subjected to artillery bombardment and suffered from shortages of food and munitions. On the 30th the battle was effectively over and Samsonov committed suicide.
The Battle of Tannenberg resulted in the destruction of almost an entire Russian army. The First Army was still intact, but it retreated shortly after its first contact with the Eighth Army in early September. While a major victory for Germany, the battle of Tannenberg did not lead to the immediate defeat of Russia. Instead, it would be followed by more battles over the next three years which would see Russia become exhausted and discontent. Eventually, the empire collapsed. The Battle of Tannenberg prevented a quick Russian victory in the east and ensured that the war would drag on. While the battle was certainly a great German victory, one wonders if it would have been better for Germany if Russia had won and forced an end to the war. Then, at least, the soldiers would have been home by Christmas.