This made it a major city in a time when Kiev, the capitol of the Kievan Rus', had a population of 50,000.
During the winter of 1237–38, the Mongol army under Batu Khan conquered the northern Rus' territories (the principalities of Ryazan and Vladimir-Suzdal) with the exception of the Novgorod Republic.
[3] In the autumn of 1239, the Mongol-Tatar horde captured Hlukhiv, Kursk, Rylsk, and Putivl and advanced towards Chernigov.
[citation needed] Following the fall of Chernigov on October 18, 1239, the Tatars pillaged towns in the surrounding countryside.
Mstislav fled to Kiev and negotiated his surrender to Batu Khan, although the terms are unclear.