Authors: D. Niceolle and V. Shpakovsky.
Title: Osprey Campaign No. 98: Kalka River 1223.
Publisher: Osprey Publications.
Price: $19.95 (US).
This book covers Subodei's raid into Russia in 1223. The Russian army and its Polotsvian allies were lured into a trap by the retreating Mongols, only to be snared on the banks of the Kalka River on the steppes of the Ukraine. Most of the Russian princes were either captured or killed. The survivors were bound and slowly suffocated to death beneath the Mongols' victory feast.
The Russians had made the mistake of killing the Mongol ambassadors when they first demanded the fleeing Polotvsians, who were allied to the Russians by treaty and marriage. Not being able to outfight the Mongol hordes, the Russians would have been better off submitting to Genghis Khan while the Mongols were still at a distance. Alas, that didn't happen.
The Mongols considered the killing of emissaries to be unpardonable. They got their revenge after the battle of the Kalka River. However, the 40,000 strong Mongol army was called back by Genghis Khan to help finish off the northern Chinese kingdom. It was up to Ogedei, Genghis Khan's son, to destroy the Russians in 1237.
Though I still think things would have gone better for the Russians if they'd first submitted to the Mongols when they first came in 1223. The subsequent dark ages wouldn't have been so oppressive or barbaric.
Recommended reading for starting with the Mongol invasions of Russia.