 The Bulgars retreated and the Mongols pursued them.Then the main Bulgar forces ambushed the Mongols.Timeline for the Expedition of Subutai and Jebe (the Mongol reconnaissance of the western steppes)

• 12 January 1221 Muhammad II of Khwarezm Shah of Khwarezm dies on the run from the Mongols on the island of Abeskum during Jenghiz Khan’s destruction of the Khwarezmid Empire campaign

• Jenghiz Khan summons his general Subutai to Samarkand upon hearing the news of the Shah’s death; Subutai gives a report on how best to defeat the new Shah, Jalal ad-Din (Muhammed’s son); Subutai requests not to be part of the final campaign and proposes to reconnoiter the west bank of the Caspian Sea and the steppes beyond - Jenghiz accepts this plan and assigns two "tumens" (20,000 men) to Subutai and his other best general, Jebe, under the condition that the campaign not take more than two years and that on their return march they find and join with the Khan’s son Jochi in the east to engage the Volga Bulgars

• Subutai rejoins Jebe at their camp near the Caspian (delta of the Kura river) - the “reconnaissance in force” begins at the end of February 1221

• the Mongols invade Georgia and annihilate George IV of Georgia’s much larger forces on the plain of Khuman

• the Mongols sack Margha and Hamadan

• the Mongols move into Georgia again towards Derbend and are attacked by King George IV with another army - the Mongols destroy it and George IV escapes with only his rearguard

• the Mongols cross the Caucasus with great hardship in winter to the Fergana valley and are to find a 50,000 man army waiting for them of Cumans assembled by their khagan Kotian and his Bulgar, Khazar, and Avar allies under the command of Kotian’s brother Yuri and son Daniel

• the Mongols engage the Cumans but can make no headway due to their unfavorable position and they withdraw - the Mongols resort to bribing the Cumans with half of their spoils taken from Georgia if they will join them - the Cumans agree but after taking payment they break camp under darkness and leave their allies

• the Mongols attack and destroy the remaining Cuman allied forces and impress those survivors considered useful into their army

• the Mongols with great speed overtake the Cumans who had fled towards Astrakhan on the Volga and extirpate them - both Yuri and Daniel are killed and the Cumans massacred to a man - the Mongols recover their treasure used in the ‘bribe’ - on news of this defeat many Cumans flee west to the borders of Hungary and the Byzantine Empire's trading station on the Sea of Azov

• the Mongols sack Astrakhan

• Subutai and Jebe split their force - Jebe marches west to the river Don to await Subutai who marches south to the Sea of Azov to ensure the Cumans cannot threaten their expedition from the rear - Subutai's force destroys the towns along the shore and what Cumans they find and meet Venetian merchants from Europe for the first time - he makes a pact with them to destroy Genoese trading posts in exchange for information on the West and military intelligence on the kingdoms there

• Jebe makes an alliance with the chief of the Brodniki, Polskinia, and 5,000 Brodniki troops join his forces on the Don

• Subutai destroys the Genoese trading station of Soldaia (Sudak) on the Crimea, then rejoins Jebe - their army now has perhaps 25,000 men - they march unopposed to the Dniester river

• Autumn and Winter 1222 - the Mongol army marches up and down the Dniester using terror tactics to maintain security from attack - scouting parties are sent as far west as possible to gather military intelligence on southern Russia and the states along the borders of the Carpathian mountains

• their objective completed, the Mongols begin the march home to Mongolian territory

• Kotian had fled north with the remnants of such Cumans as he could and was pleading for an alliance with the Russian princes against the Mongols - at a conference the Russian princes of Galicia (Mstislave the Daring), his son-in-law Daniel of Volynia, Prince Oleg of Kursk, and the Princes of Kiev and Chernigov agree to join Kotian to stop the Mongols - Duke Yuri of Suzdal promises to send an army under the command of his nephew the Prince of Rostov - the nominal strength of this allied force was 80,000 men

• the Mongols are aware via their spies and scouts that a military action is being planned against them - the allied Russian and Cuman forces are approaching from several directions

• the Mongols cross the Dnieper where the expected rendezvous with Jochi does not take place - Jochi is supposedly ill in the east and is delayed

• the Mongols send ambassadors to the Princes of Chernigov and Kiev to attempt peace - the Russians kill the ambassadors - a second Mongol embassy arrives to declare war

• the Mongols were still under the Khan's orders to suppress the Volga Bulgars, but this cannot be safely done with enemies in their rear - the elimination of the Russian threat was a military necessity

• Subutai and Jebe leave 1,000 men under the command of Hamabek on the east bank of the Dnieper to delay the Russian crossing for as long as possible - this rearguard was able to inflict heavy casualties but was eventually overwhelmed and destroyed and Hamabek was captured and executed

• May 1223 - the Mongols are slowly retreating over land they had excellent knowledge of north of the Sea of Azov - their mobility allowed them to easily outpace the Russian forces but they had decided on a confrontation with them - on 31 May 1223 they stopped along the western side of the river Kalka (Kalmyus)

• Battle of the Kalka River - the Mongol forces, numbering at this point perhaps 23,000 - exterminate the combined Cuman-Russian armies - some 40,000 Russian and Cuman soldiers are killed - the Mongol tactics and weaponry, with which the Russians had no prior experience, are superior to the rather unorganized assault by the allied armies - the Mongols pursue the remnants of the allied forces to the Dneiper

• the Prince of Kiev had retreated with his army mostly intact back to the Dnieper, not having been part of the reckless charges at Kalka; however they were overtaken by the Mongols and eventually massacred in their fortified camp

• the Prince of Rostov stopped and returned with his army to Suzdal upon the news of the defeat at Kalka to prepare for an attack, but it never came - the Mongols had resumed their march east 

This Mongol campaign had killed perhaps as many as 200,000 soldiers of various nations and never lost a major battle.