1. An ancient region of east-central Asia comprising modern-day Inner Mongolia and the country of Mongolia. The Mongol tribes in the region were united in the 1200s by Genghis Khan. After the 1600s, China and Russia contended for control of the area, with the southern part eventually joining China.
2. Formerly Outer Mongolia. A country of north-central Asia between Russia and China. Originally part of the Mongol Empire, the area was under Chinese control from 1691 to 1911 and from 1919 to 1921, when it formed a separate state under the protection of the USSR. Ulaanbaatar is the capital and the largest city.