During the Yuan Dynasty, the predecessor of Tsarist Russia, that is, the Kiev Principality, was a vassal of Qinchahan (or Golden Account Khan) in the Four Great Khan Countries of the Yuan Dynasty, that is to say, the sovereignty of Kiev Principality belonged to Qinchahan, and Qinchahan was a vassal of the Yuan Dynasty, so the status of the Yuan Dynasty was much higher than that of Kiev Principality, and its territorial sovereignty belonged to Qinchahan, not to mention the dividing line with the Yuan Dynasty.
But if we insist on dividing it, the territory of Kiev at that time was today's Kiev and Moscow, the capital of Ukraine, located in the eastern European plain, and the dividing line with the Yuan Dynasty was today's Black Sea to the Don River and the Volga River.