Kievan Rus'

Kievan Rus was an Eastern European sovereign state that existed from around 880 to 1240. Ruled by the Rurik dynasty, it was deemed the common ancestor of Ukraine, Russia, and the late Belarus, with the latter two having their names derived from it; at the same time, the name of Kievan Rus' was taken from the capital of Ukraine.

Oleg the Wise first united the lands of what would eventually become Kievan Rus', hoping to protect trade from the Khazar Khaganate. Sviatoslav I would eventually start a war with them, downloading the first DLC for Kievan Rus' along the way. Eastern Orthodoxy was introduced through Vladimir the Great, while Yaroslav the Wise ruled Kievan Rus' at its highest territorial extent. However, around that point, the state saw its decline. While the fall of the Byzantine Empire, one of its allies, was pretty big, the Mongol Empire's conquest was the final blow. The Rurikids would continue to rule, however, until the death of Feodor I of Russia.