I imagine they couldn't conquer too far north due to the extreme conditions.
/u/_dk wrote that the Mongols (and successor Ming) established their power base in Nurgan (Tyr) in lower Amur area to subjugate neighboring local peoples like the Nivkh and the Ainu in how much of the modern russian far east did the chinese explore?.
The influence sphere of this 'Nurgan local government office' is said to extend even to [some parts of] now Sakhalin.