After the initial round of war declarations, events unfolded quickly as each side tried to position itself advantageously. Germany’s troops were the first to move, and their initial target was Belgium. The first German troops crossed the border on the night of August 3, 1914, expecting to overtake the little nation quickly and to move on to their main objective of France.
The Germans found more resistance than anticipated, however, especially among civilian snipers who fired on them from hidden positions. In retaliation, the Germans burned a number of towns and villages to the ground and executed large numbers of civilians, including women and children. The heaviest fighting was around the fortress at Liege; the capital, Brussels, did not fall until August 20. All the time, however, additional German armies were gathering along the remainder of France’s eastern borders.
Undermining Germany’s Schlieffen Plan, Russian troops attacked Germany much sooner than expected. Two Russian armies, under generals Alexander Samsonov and Paul von Rennenkampf, crossed Germany’s border in East Prussia on August 17. With the brunt of German forces focused on France, the Russians advanced quickly at first and soon threatened the regional capital of Königsberg (present-day Kaliningrad).
Vastly outnumbered and initially overwhelmed, the German commander in the region, General Maximilian von Prittwitz, panicked and tried to call a retreat, against the advice of his staff. To deal with the emergency, German military leaders quickly replaced Prittwitz with a more experienced leader, General Paul von Hindenburg, and recalled some of the troops from the western front to help in the east.
Reinforced and under new leadership, the German forces in the east struck back decisively at the invading Russian forces. Because the armies of Samsonov and Rennenkampf were operating separately, without mutual coordination, the Germans were able to deal with them one at a time. Two German armies engaged Samsonov’s forces at Tannenberg on August 26. Eventually, weakened by constant pounding from German artillery, Samsonov’s troops were forced to retreat. As they did so, a second German army cut off their path, completely entrapping them. A slaughter ensued in which over 30,000 Russian soldiers were killed and an additional 92,000 taken prisoner. General Samsonov committed suicide that same day.
On September 9, Hindenburg’s troops took on Rennenkampf’s army at the nearby Masurian Lakes, for a near repeat performance of Tannenberg. Though Rennenkampf’s army did manage to retreat successfully, they did so only with another 125,000 casualties. Between Tannenberg and the Masurian Lakes, Russia lost approximately 300,000 soldiers in less than a month of fighting.