The defeat at the Kalka River had…

The defeat at the Kalka River had left the Kievan principality at the mercy of invaders, but the Mongol forces had retreated, not to reappear for thirteen years, during which time the princes of Rus' have gone on quarreling and fighting as before, until they are startled by a new and much more formidable invading force.

The main Mongol force, headed by Jochi's sons, and their cousins, Möngke Khan and Güyük Khan, arrive at Ryazan in December 1237.

Ryazan refuses to surrender, and the Mongols sack it.

The Principality is completely overrun with almost the whole princely family killed and the capital completely destroyed; it will later be moved to another location.