Vladimir Putin Held A Training Session In Judo, St. Petersburg, Russia

In the 10th to 11th centuries Kievan Rus' became one of the largest and most prosperous states in Europe. The reigns of Vladimir the Great (980–1015) and his son Yaroslav I the Wise (1019–1054) constitute the Golden Age of Kiev, which saw the acceptance of Orthodox Christianity from Byzantium and the creation of the first East Slavic written legal code, the Russkaya Pravda.
In the 11th and 12th centuries, constant incursions by nomadic Turkic tribes, such as the Kipchaks and the Pechenegs, caused a massive migration of Slavic populations to the safer, heavily forested regions of the north, particularly to the area known as Zalesye.
The age of feudalism and decentralization had come, marked by constant in-fighting between members of the Rurik Dynasty that ruled Kievan Rus' collectively. Kiev's dominance waned, to the benefit of Vladimir-Suzdal in the north-east, Novgorod Republic in the north-west and Galicia-Volhynia in the south-west.
Ultimately Kievan Rus' disintegrated, with the final blow being the Mongol invasion of 1237–40, that resulted in the destruction of Kiev and the death of about half the population of Rus'. The invaders, later known as Tatars, formed the state of the Golden Horde, which pillaged the Russian principalities and ruled the southern and central expanses of Russia for over three centuries.