Mongol invasion of Rus'

Mongol conquest of Eastern Europe
The Genghis Khan conquests
Date 1223–1240 Location Modern Russia, Ukraine and Belarus Result Decisive Mongol victory resulting in principalities of Kievan State becoming vassals of the Mongol Golden Horde.
Belligerents
Mongol Empire	Vladimir-Suzdal Kiev Galicia-Volhynia Novgorod Republic Smolensk Turov and Pinsk Rostov Chernigov Ryazan Pereyaslavl Cumans
Commanders and leaders
Batu Khan Möngke Khan Subutai Jebe Boroldai Berke Orda Kadan Shiban Güyük Khan	Mstislav the Bold Daniel of Galicia  Mstislav III of Kiev  (POW),   Mstislav II of Chernigov  † Yuri II of Vladimir  †
Strength
20,000 in 1223 In 1236, More than 35,000 Mongols+More than 40,000 Turkic auxiliaries	80,000 in 1223
Casualties and losses
More than 7,000	500,000 (6–7% of the population of Rus)

As part of the Mongol invasion of Europe, the Mongol Empire invaded Kievan Rus' in the 13th century, destroying numerous cities, including Ryazan, Kolomna, Moscow, Vladimir, and Kiev.

The campaign was heralded by the Battle of the Kalka River in May 1223, which resulted in a Mongol victory over the forces of several Rus' principalities. The Mongols nevertheless retreated. A full-scale invasion of Rus' by Batu Khan followed, from 1237 to 1240. The invasion was ended by the Mongol succession process upon the death of Ögedei Khan. All Rus' principalities were forced to submit to Mongol rule and became part of the Golden Horde empire, some of which lasted until 1480.

The invasion, facilitated by the beginning of the breakup of Kievan Rus' in the 13th century, had incalculable ramifications for the history of Eastern Europe, including the division of the East Slavic people into three separate nations, modern-day Russia, Ukraine, and Belarus, and in the rise of the Grand Duchy of Moscow.

As it was undergoing fragmentation, Kievan Rus' faced the unexpected eruption of an irresistible foreign foe coming from the mysterious regions of the Far East. "For our sins", writes the Rus' chronicler of the time, "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".

The princes of Rus' first heard of the coming Mongol warriors from the nomadic Cumans. Previously known for pillaging settlers on the frontier, the nomads now preferred peaceful relations, warning their neighbors: "These terrible strangers have taken our country, and tomorrow they will take yours if you do not come and help us". In response to this call, Mstislav the Bold and Mstislav Romanovich the Old joined forces and set out eastward to meet the foe, only to be routed on April 1, 1223 at the Battle of the Kalka River.

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Wikipedia