 Complete the following phrase:  Ögedei Khan ordered Batu Khan to conquer Rus in 1235. The main force, headed by Jochis sons, and their cousins, Möngke Khan and Güyük Khan, arrived at Ryazan in December 1237. Ryazan refused to surrender, and the Mongols sacked it and then stormed Suzdalia. Many Rus armies were defeated; Grand Prince Yuri was killed on 