Principality of Novgorod-Seversk
The Principality of Novgorod-Seversk was a medieval Rus' principality centered on the town now called Novhorod-Siverskyi. The principality was aligned to the Principality of Chernigov. It may have been created in 1139, the date of one modern authority. In 1185, a large Rus'ian campaign against the Polovtsy ended in defeat for Prince Igor, famously recorded in The Tale of Igor's Campaign. The principality was taken by the principality of Briansk after the Mongol invasions, and then by the Lithuanians when the power of the Golden Horde began to decline. In the fifteenth-century the principality was given to Prince Ivan of Mozhaisk when he fled from Grand Prince Vasily II.
See also 
- Martin, Janet, Medieval Russia, 980-1584, (Cambridge, 1995)