It is will be true that the land, habituated by Mongols before Manch and Russian rule is the historical motherland of Mongols. Mongolian territory in medievel time lasted to Lyadun galp, Great white wall, Gobi, Khokhnuur, Sunzaan, Erchis river, Baikal and Hungan mountain. Mongolia is a huge country spanning over of some 3.5 million square kilometers (Mongolia, Inner Mongolia, Transbaikal), a bit larger in area than.
Great Plains with 3.4 million square kilometers. Its first unification came in 209 when Maodun Shanyui of Huns formed the first state on Mongolian territory. For three centuries, Hunish empire was equal and feared rival of Han China, but it disintegrated and fell by 100 AD.
Mongolia was reunited by great leader Tanshihuai of the Xianbie Mongols in the middle of 2 century AD. After his death steppes again disunited. By middle of 4 century, Tabgach Mongols firmly occupied all of Mongolia and began conquest of Birth Chinawhere they founded Toba-Wei dynasty pushing the Chinese towards south. That huge area could not ruled from Orkhon river and it soon was peacefully partitioned into Western and Eastern Khanates and Mongolia became the main base of the latter.
By middle of 7 century, the Tang empire conquered all of MOngolia and ruled it for half a century. But the Turks finally revolved under their leader Kultegin and founded Second Turkey Khanate in 690. The resurgent khanate lasted only 50 years after which the Uyghur Turks founded their own state in Mongolia, the Uyghur Khanate./ Uyghur Empire lasted a century after which the Yenisei Kirgiz destroyed it in 840s and established bried Jrigiz Khanate. It soon disintegrated and Mongolia once again fell into long period of anarchy.
During the following three centuries however, most of Mongolia came under suzerainty of Khitan Mongols empire of Manchuria and North China and its successor Jurchid empire.
Finally, in 1206, Chinggis Khan united Mongols, destroyed Jurchids and brought all of Eurasian Great Steppe under his rule Great Mongol empire by 1260 was partitioned into four Khanates which ruled almost all of Eurasian Great Steppe. After end of Yuan dynasty, Mongolia briefly became disintegrated by 1400. But it was reunited several times during the next century, last time by Bayan Khan, who ruled Mongolia till 1543. After which Altan Khan ruled most of Mongolia till 1580s. And from then on there was no unity in 1636, northern Mongolia by 1698 and western Mongolia by 1757, Baikal region they did not get since the Russians took it by 1650s.
Mongolia remained united under Manchus till 1911 when China annexed southern part of Mongolia. Northern part became independent country which was united ever since.