The city prospered again during the Russian Empire's Industrial Revolution in the late 19th century. In 1918, after the Ukrainian People's Republic declared independence from Soviet Russia, Kyiv became its capital. From 1921 onwards Kyiv was a city of Soviet Ukraine, which was proclaimed by the Red Army, and, from 1934, Kyiv was its capital. The city was almost completely ruined during World War II but quickly recovered in the postwar years, remaining the Soviet Union's third-largest city.