 Complete the following phrase:  Batu Khan, another grandson of Genghis Khan, overran the territories of the Bulgars, the Alans, the Kypchaks, Bashkirs, Mordvins, Chuvash, and other nations of the southern Russian steppe. By 1237 the Mongols were encroaching upon Ryazan, the first Kievan Rus principality they were to attack. After a three-day siege involving fierce fighting, the Mongols captured the city and massacred its inhabitants. They then proceeded to destroy the army of the Grand Principality of Vladimir at the 