Rennenkampf gained a reputation as an effective cavalry commander during the Boxer Rebellion and the Russo-Japanese War. Following service in the latter, he led the detachment that suppressed the Chita Republic during the 1905 Russian Revolution. This earned him further promotion, and by the outbreak of World War I Rennenkampf was commander of the Vilna Military District, whose forces were used to form the 1st Army under his command. He led the 1st Army in the invasion of East Prussia and won an early victory at Gumbinnen in late August 1914, but was relieved of command after defeats at Tannenberg, the Masurian Lakes and Łódź, although he was later proved innocent for the mistakes made in the Battle at Łódź. Exonerated by an official inquiry into his actions, Rennenkampf was shot by the Bolsheviks in Taganrog during the Red Terror in 1918.