Cossacks were simultaneously both an ethnicity and a grouping of special social estates in the Russian Empire from the 16th to the early 20th century. Because of their military tradition, Cossack forces played an important role in Russia's wars of the 17th–20th centuries such as the Crimean War (1853-1856), the Napoleonic Wars, various Russo-Turkish Wars, and the First World War of 1914-1918. In the late-19th and early-20th centuries, the tsarist regime deployed Cossack detachments to perform police service and to suppress revolutionary movements, especially in 1905–1907.