The Mongol Empire invaded and conquered much of the Kievan Rus' in the mid-13th century, sacking numerous cities such as Ryazan, Yaroslavl, Pereyaslavl and Vladimir, including the largest: Kiev (50,000 inhabitants) and Chernigov (30,000 inhabitants). The siege of Kiev in 1240 by the Mongols is generally held to mark the end of the state of Kievan Rus', which had already been undergoing fragmentation. Many other principalities and urban centres in the northwest and southwest escaped complete destruction or suffered little to no damage from the Mongol invasion, including Galicia–Volhynia, Pskov, Smolensk, Polotsk, Vitebsk, and probably Rostov and Uglich.

The Mongol campaign was heralded by the Battle of the Kalka River on 31 May 1223, which resulted in a Mongol victory over the forces of several principalities as well as the remnants of the Cumans under Köten. The Mongols retreated, having gathered their intelligence, which was the purpose of the reconnaissance-in-force. A full-scale invasion by Batu Khan followed, with most of Kievan Rus' overrun in 1237–1238. The Mongols captured Kiev in 1240 and moved west into Hungary and Poland. The heavy losses suffered by the Mongols during the invasion period significantly weakened subsequent campaigns, preventing the ruin of the Holy Roman Empire and more western countries.

The invasion was ended by the Mongol succession process upon the death of Ögedei Khan. Even those principalities who avoided physical conquest were eventually forced to accept Mongol supremacy in the form of tribute – as in the case of Galicia–Volhynia, Polotsk and Novgorod – if not outright vassalage, of the Golden Horde, until well into the 14th century. Although a Russian army defeated the Mongols at the Battle of Kulikovo in 1380, the Mongolian demands of tribute from Russian princes continued until about 1480.

The Mongols had plans to conquer Eastern Europe long before Batu's campaign in 1237. In 1207, Genghis Khan sent his eldest son Jochi to conquer the tribes north of the Selenga River and in the Irtysh valley, which included the lands of Eastern Europe in the Jochi Ulus. However, these plans were not implemented during the lifetime of Genghis Khan. In 1222–1224, Subutai and Jebe conducted a campaign with a 30,000-strong army in Transcaucasia and Southeastern Europe, which is traditionally considered as a reconnaissance. However, the Secret History of the Mongols and Rashid ad-Din state that the purpose of this campaign was to be supported by the forces of Jochi and included Cumania, Alania, Hungary, and Rus', including Kiev. The kurultai of 1235, after which the invasion of Europe took place, repeated these goals. The campaign of Subutai and his 30,000 troops to the Caspian steppes was a new step in the conquest of Eastern Europe, and it began in the late 1220s. In 1235, a kurultai was convened to outline a general Mongol campaign, in which the troops of other uluses (clans or tribes) were to take part. Ögedei sent Batu, Büri, Möngke, and other princes on a campaign to help Subutai, and each Chingizid led with him one or more tumens of the army. The Mongols prepared for an offensive in 1235 and early 1236 and subjugated the Bashkir tribes, who were forced to allocate several detachments to the Mongol army. The Mongols concentrated in the Caspian steppes in the autumn of 1236 under the general leadership of Jochi's son Batu. The first blow of the united Chingizid army targeted Volga Bulgaria.

The princes of Galicia–Volhynia and Chernigov initially defeated the Mongols at Battle of Oleshia in May 1223. The Mongols (called "Tartars" in contemporary accounts) then defeated a united Rus' army led by Mstislav the Bold and Mstislav Romanovich the Old on 31 May 1223 at the Battle of the Kalka River. In 1237, they besieged and took Ryazan, and Vladimir fell in early February 1238. "For our sins", wrote a chronicler, "unknown nations arrived. No one knew their origin or whence they came, or what religion they practiced. That is known only to God, and perhaps to wise men learned in books". Although this defeat left the principalities at the mercy of invaders, the Mongol or Tartar forces retreated and did not reappear for another 13 years, during which time the princes of Rus' went on quarreling and fighting as before, until they were startled by a new and much more formidable invading force. In The Secret History of the Mongols, the only reference to this early battle is:

Then he (Genghis Khan) sent Dorbei the Fierce off against the city of Merv, and on to conquer the people between Iraq and the Indus. He sent Subetei the Brave off to war in the North where he defeated eleven kingdoms and tribes, crossing the Volga and Ural Rivers, finally going to war with Kiev.^{[citation needed]}

The Secret History of the Mongols reports that Ögedei sent Batu, Büri, Möngke, and many other princes on a campaign to help Subutai, who was facing strong resistance from various peoples and cities under Genghis Khan's command. The list of Genghisides who participated in the campaign is present in works such as The Secret Legend, Yuan Shi, and Jami' al-tawarikh. In addition to Batu, other Chingizids who participated in the campaign included the sons of Jochi, Orda, Shiban, Tangkut and Berke; the son of Chagatai, Baidar, and the grandson of Chagatai, Büri; the sons of Ögedei, Güyük and Kadan; the sons of Tolui, Möngke and Ariq Böke; the son of Genghis Khan, Külkhan, and the grandson of Genghis Khan's brother, Argasun. In 1235 and early 1236, the assembled army prepared for an offensive, and then subjugated the Bashkir tribes, who were forced to allocate several detachments to the Mongol army. In the autumn of 1236, the Mongols concentrated on the Caspian steppes under the general leadership of Jochi's son Batu.

The first blow of the united Chingizid army struck Volga Bulgaria. Until the mid-1220s, Volga Bulgaria was in constant conflict with the Vladimir-Suzdal and Murom-Ryazan principalities. The parties undertook campaigns, there were constant skirmishes, the victories in which were mainly won by Rus' troops. However, with the appearance of the Mongols at their borders, the Bulgars began to seek peace, which was met with understanding and support from the Rus' princes. Over the course of several years, the Rus' and the Bulgars normalized relations, which allowed the Volga Bulgaria to devote all its forces to preparing to repel the alleged Mongol invasion. Ramparts were created in the forests that covered the main cities, the cities themselves were fortified, and the garrisons increased. However, all these measures were in vain – the Volga Bulgaria was defeated with lightning speed and completely conquered by the spring of 1237.^{[citation needed]}