The Battle of the Kalka River[a] was fought between the Mongol Empire, whose armies were led by Jebe and Subutai, and a coalition of several Rus' principalities, including Kiev and Galicia-Volhynia, and the Cumans under Köten.

The battle was fought on May 31, 1223 on the banks of the Kalka River in present-day Donetsk Oblast, Ukraine, and ended in a decisive Mongol victory.

Jebe requested permission from the Mongol emperor, Genghis Khan, to continue his conquests for a few years before returning to the main army via the Caucasus.

The Cuman Khan fled to the court of his son-in-law, Mstislav Mstislavich of Galicia, whom he convinced to help fight the Mongols.

Mstislav the Bold and his Cuman allies attacked the Mongols without waiting for the rest of the Rus' army and were defeated.

In the ensuing confusion, several other Rus' princes were defeated, and Mstislav of Kiev was forced to retreat to a fortified camp.

[12] In a campaign that lasted three years, Genghis Khan and his generals destroyed the Khwarezmian armies and caused the empire to disintegrate.

[14] They left behind a trail of destruction as they moved through Persian Iraq (Iraq-i Ajam) and Azerbaijan, sacking the cities of Rey, Zanjan and Qazvin.

However, the King of Georgia, George IV Lasha, advanced with 10,000 men and drove the Mongols back near Tbilisi.

In March 1221, the Mongols returned to Azerbaijan and besieged Maragheh, using prisoners as the vanguard to take the brunt of each assault on the city.

The Georgian cavalry pursued Subutai's army after defeating the Turkmen and were destroyed when Jebe closed the trap.

[20] Genghis Khan eventually granted Jebe permission and with Subutai as his second-in-command,[14] the Mongols advanced to the city of Derbent, which refused to surrender.

The crossing of the Caucasus was costly for the Mongols, who had to abandon their siege engines and lost hundreds of men to the cold.

[22] They were joined by the Cumans, a Turkic people who had an expansive khanate stretching from Lake Balkhash to the Black Sea.

The Mongols then proceeded to attack the Cumans, who had split into two separate groups as they were returning home, destroying both armies and executing all the prisoners before sacking Astrakhan.

Khrustalev estimated in 2013 that the Rus' army consisted of 10,000 soldiers (including mercenaries), while the Cumans brought 5,000 cavalry, for a total of 15,000.

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

Mstislav of Kiev had the envoys executed, and the Mongols responded by sending another set of ambassadors, who declared war.

As to the actual battle itself, the chronicles report that the Polovtsy (Cumans) broke and ran without having fought and that their flight through the Rus’ ranks led to mass confusion and resulted in their slaughter by the Mongols.

The Mongols appear to have caught the coalition forces by surprise in a fast transition from horse archer fire to massed cavalry charges, because the coalition rout began incredibly quickly: the Rus forces bringing up the rear had not yet arrived on the battlefield by the time the front ranks were dissolving.

[28] The battle was a very costly defeat for the Rus' princes, with Richard Gabriel claiming that they lost 50,000 men, while the Mongol losses were minimal.

The Novgorodian First Chronicle (the most reliable), contemporary to the battle, gives no figures at all, but does say that only 1 in 10 soldiers made it back home, suggesting the number of killed was equivalent to almost the entire army.

[38] Historian Robert Marshall describes the raid as follows: "The rest of Subutai's campaign has entered the annals of military history as one of the greatest adventures of cavalry warfare.

[41] After the battle, the people of Rus trembled in fear of this unknown scourge who had emerged from the frontier and destroyed the flower of their army.

What the Rus' feared would happen did not come to pass, as the Mongols pursued the prince of Galicia and plundered a few towns in the south before turning around.

They fought against the Cuman army near the Ural Mountains, defeating and killing the Khan before making them pay tribute.