Kyiv prospered during the late 19th century Industrial Revolution in the Russian Empire, when it became the third most important city of the Empire and the major centre of commerce of its southwest. In the turbulent period following the 1917 Russian Revolution, Kyiv became the capital of several successive Ukrainian states and was caught in the middle of several conflicts: World War I, during which German soldiers occupied it from 2 March 1918 to November 1918, the Russian Civil War of 1917 to 1922, and the Polish–Soviet War of 1919–1921. During the last three months of 1919, Kyiv was intermittently controlled by the White Army. Kyiv changed hands sixteen times from the end of 1918 to August 1920.