The Rus princes have ignored the Cumans’ warnings for almost a year, as the Rus have suffered from Cuman raids for decades, but when news reaches Kiev that the Mongols are marching along the Dniester River, the Rus respond.

Mstislav gathers an alliance of the Kievan Rus' princes including Mstislav III of Kiev and Prince Yuri II of Vladimir-Suzdal, who promise support.

The Rus princes then begin mustering their armies and going towards the rendezvous point.

The move by the Rus' army is detected by the Mongols, who are on the east side of the Dnieper River waiting for reinforcements from Jochi, Genghis Khan's eldest son, who is campaigning around the Aral Sea.

Jochi, however, has become ill, which means no reinforcements will be coming.

At the same time, the Rus' attempt to trap the Mongols.

The Princes of Galich and Volhynia transport their armies south down the river, while the Princes of Kiev and Chernigov advance north up the river, and the army of Kursk advances from the front.

At the same time, the Cumans attempt to attack the Mongol army's rear.

When Jebe learns of this, he sends ten envoys to the Prince of Kiev.

The envoys state that the Mongols have no feud with Rus and are only attacking the Cumans; they add that the Mongols are marching east, away from the Rus' cities.

Mstislav of Kiev has the envoys executed, and the Mongols respond by sending another set of ambassadors, who declare war.

When Jebe and Subutai hear of the Rus' movements, they begin moving east, away from Rus', which is the only direction in which they can move.

However, they leave a rearguard of one thousand under the command of an officer, Hamabek, to report of the Rus movements.

Soon, Mstislav the Bold reaches the river opposite the rearguard, and it becomes apparent that no Prince had been appointed commander-in-chief.

Thus, all the Princes can act as they pleased.

Eventually, Mstislav crosses the river under heavy arrow fire.

When the Rus' land, however, their numbers are far superior, and the Mongols are killed to the last man.