Principality of Chernigov
In 1024, while Yaroslav the Wise was away from Kiev, Mstislav led his army, which included Kassogian and Khazar troops, against Kiev. Although he could not enter the capital of Rus' because of the locals' opposition, he forced the Severiansan East Slavic tribe dwelling along the Desna River to the east of Kievto accept his suzerainty. He transferred his seat from Tmutarakan to Chernihiv, which was the second largest town in Kievan Rus'. For no source mentions a local prince ruling in Chernigov before this event, historians regard Mstislav as the first ruler of the Principality of Chernigov. He had the citadel expanded and the defensive works surrounding the suburb reinforced in his new seat.