From the 16th to 19th centuries, Russian Cossacks played a key role in the expansion of the Russian Empire into Siberia (particularly by Yermak Timofeyevich), the Caucasus, and Central Asia. Cossacks also served as guides to most Russian expeditions of civil and military geographers and surveyors, traders, and explorers. In 1648, the Russian Cossack Semyon Dezhnyov discovered a passage between North America and Asia. Cossack units played a role in many wars in the 17th, 18th, and 19th centuries, including the Russo-Turkish Wars, the Russo-Persian Wars, and the annexation of Central Asia.