Kievan Rus was a loose federation of Slavic lands that had coalesced from the 9th century. This loose Federation of city-states was held together by the family bonds of the ruling princes. The Ruikovichi, who were descended from the Varangian chieftain, Rurik. Vladimir (r. 980-1015) ruled from Kiev, and his twelve sons were the princes of the largest cities in Rus. It was Vladimir who ordered the mass conversion of Kievan Rus to Orthodox Christianity. The first onslaught of the nomadic Mongols, a collection of Turkic tribes who originated in present-day Mongolia, took them to the southern steppes of Russia. Some of the Kievan princes joined forces to defend their territory against the Mongols, but were crushed at the Battle of the Kalka River (1223). By 1240 the Mongols had advanced deep into the heart of Russia. The Kievan princes surrendered, along with the Republic of Novgorod, which was spared pillage because its prince had accepted his Mongol overlords. The Mongols ruled in Russia for 200 years, accepting tax and tributes and expecting their subjects to provide armies, but otherwise allowing the princes to govern their own territories.
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