Great hordes of horsemen have repeatedly swept down from Mongolia into N China, establishing vast, although generally short-lived, empires. In the 1st cent. A.D. Mongolia was inhabited by various Turkic tribes who dwelt mainly along the upper course of the Orkhon River. It was also the home of the Hsiung-nu who ravaged (1st–5th cent.) N China. The Uigur Turks founded their first empire (744–856) with its capital near Karakorum in W Mongolia. The Khitan, who founded the Liao dynasty (947–1125) in N China, were from Mongolia. Many smaller territorial states followed until (c.1205) Jenghiz Khan conquered all Mongolia, united its tribes, and from his capital at Karakorum led the Mongols in creating one of the greatest empires of all time. His successors established the Golden Horde in SE Russia and founded the Hulagid dynasty of Persia and the Yuan dynasty (1260–1368) of China.
After the decline of the Mongol empire, Mongolia intruded less in world affairs. China, which earlier had gained control of Inner Mongolia, subjugated Outer Mongolia in the late 17th cent., but in the succeeding years struggled with Russia for control. Outer Mongolia finally broke away in 1921 to form the Mongolian People's Republic (now Mongolia). Inner Mongolia remained under Chinese control, although the Japanese conquered Rehe (1933), which they included in Manchukuo, and Chahar and Suiyuan (1937), which they formed into Mengjiang (Mongol Border Land). These areas were returned to China after World War II. In 1944, Tannu Tuva (see Tuva Republic), long recognized as part of Mongolia but under Russian influence since 1911, was incorporated within the USSR (now Russia). The Chinese Communists joined most of Inner Mongolia to N Rehe prov. and W Heilongjiang prov. to form the Inner Mongolian Autonomous Region in 1949.