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 in 1223 at the Battle of the Kalka River, a defeat remembered to this day in Russia and Ukraine.
Although this defeat left the Kievan principality at the mercy of invaders, the Mongol forces retreated and did not reappear for thirteen 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 than at Kalka.
In November 1237, Batu Khan sent his envoys to the court of Yuri II of Vladimir and demanded his submission. A month later, the hordes besieged Ryazan. After six days of bloody battle, the capital was totally annihilated, never to be restored. Alarmed by the news, Yuri II sent his sons to detain the invaders, but they were soundly defeated. Having burnt down Kolomna and Moscow, the horde laid siege to Vladimir on February 4, 1238. Three days later, the capital of Vladimir-Suzdal was taken and burnt to the ground. The royal family perished in the fire, while the grand prince hastily retreated northward. Crossing the Volga, he mustered a new army, which was totally exterminated by the Mongols in the Battle of the Sit River on March 4.
Thereupon Batu Khan divided his army into smaller units, which ransacked fourteen cities of modern-day Russia: Rostov, Uglich, Yaroslavl, Kostroma, Kashin, Ksnyatin, Gorodets, Galich, Pereslavl-Zalessky, Yuriev-Polsky, Dmitrov, Volokolamsk, Tver, and Torzhok. The most difficult to take was the small town of Kozelsk, whose boy-prince Vasily, son of Titus and inhabitants resisted the Mongols for seven weeks, killing 4,000. As the story goes, at the news of the Mongol approach, the whole town of Kitezh with all its inhabitants was submerged into a lake, where, as legend has it, it may be seen to this day. The only major cities to escape destruction were Novgorod and Pskov. Refugees from southern Rus' gravitated mostly to the northeast, in the forest region with poor soils between the northern Volga and Oka Rivers. In the summer of 1238, Batu Khan devastated the Crimea and pacified Mordovia. In the winter of 1239, he sacked Chernigov and Pereyaslav. After many days of siege, the horde stormed Kiev in December 1240. Despite the fierce resistance of Danylo of Halych, Batu Khan managed to take two of his principal cities, Halych and Volodymyr-Volynskyi. The Mongols then resolved to "reach the ultimate sea", where they could proceed no further, and invaded Hungary and Poland.
The term by which this subjection is commonly designated, the Mongol or Tatar yoke, suggests ideas of terrible oppression, but in reality these nomadic invaders from Mongolia were not such cruel, oppressive taskmasters as is generally supposed. In the first place, they never settled in the country, and they had little direct dealing with the inhabitants. In accordance with the admonitions of Genghis to his children and grandchildren, they retained their pastoral mode of life, so that the subject races, agriculturists, and dwellers in towns, were not disturbed in their ordinary avocations.
In religious matters they were extremely tolerant. When they first appeared in Europe, they were Shamanists, and as such they had naturally no religious fanaticism. Thus, after they adopted Islam they remained as tolerant as before, and the khan of the Golden Horde, who first became a Muslim, allowed the Rus to found a Christian bishopric in his capital. Nogai Khan, half a century later, married a daughter of the Byzantine emperor, and gave his own daughter in marriage to a Rus prince, Theodor the Black. Some modern Russian historians (most notably, the Soviet era historian and "Neo-Eurasianist" ideologist Lev Gumilev) even postulate there was no invasion at all. According to them, the Rus princes concluded a defensive alliance with the Horde in order to repel attacks of the fanatical Teutonic Knights, which posed a much greater threat to Rus religion and culture.
These represent the bright side of Tatar rule. It had its dark side also. So long as a great horde of nomads was encamped on the frontier the country was liable to be invaded by an overwhelming force. Fortunately, these invasions were not frequent but when they occurred they caused an incalculable amount of devastation and suffering. In the intervals the people had to pay a fixed tribute. At first it was collected in a rough-and-ready fashion by Tatar tax-gatherers, by about 1259 it was regulated by a census of the population, and finally its collection was entrusted to the native princes, so that the people were no longer brought into direct contact with the Tatar officials.
Historians have debated the long-term influence of Mongol rule on Rus society. The Mongols have been blamed for the destruction of Kievan Rus', the breakup of the ancient Rus nationality into three components, and the introduction of the concept of "oriental despotism" into Russia. But some historians agree that Kievan Rus' was not a homogeneous political, cultural, or ethnic entity and that the Mongols merely accelerated fragmentation that had begun before the invasion. Historians also credit the Mongol regime with an important role in the development of Muscovy as a state. Under Mongol occupation, for example, Muscovy developed its mestnichestvo hierarchy, postal road network, census, fiscal system, and military organization.
Certainly, it can be (and often is) argued that without the Mongol destruction of Kievan Rus' that Moscow, and subsequently the Russian Empire, would not have risen. Trade routes with the East came through the Rus lands, making them a center for trade from both worlds. In short, the Mongol influence, while destructive in the extreme to their enemies, had a significant long term effect on the rise of modern Russia, Ukraine and Belarus.
A significant number of historians consider the oppression of Rus' by the Mongols to be the major cause of what is sometimes called "the East-West gap" - approximately 200 years delay in introducing major social, political and economical reforms and scientific innovations in Russia comparing to Western Europe. Some argue that the yoke had a severe destructive influence on the delicate system of unwritten laws regulating everyday life of society. For instance, Valeriya Novodvorskaya mentions that the death penalty, long-term imprisonment and tortures had not existed in Rus' before the Mongols invaded the country. Over half the population of Rus may have died during the Mongol invasions. Colin McEvedy (Atlas of World Population History, 1978) estimates the population of Russia-in-Europe dropped from 7.5 million prior to the invasion to 7 million afterwards.
The period of Mongol rule over Russia included significant cultural an interpersonal contacts between the Russian and Mongolian ruling classes. By 1450, the Tatar language had become fashionable in the court of the Grand Prince of Moscow, Vasily II, who was accused of excessive love of the tatars and their speech. Many Russian boyar (noble) families traced their descent from the Mongols or Tatars, including Veliaminov-Zernov, Godunov, Arseniev and Bakhmetev. In a survey of Russian noble families of the 17th century, over 15% of the Russian noble families had Tatar or Oriental origins. In the religious sphere, St. Paphnutius of Borovsk was the grandson of a Mongol baskak, or tax collector, while a nephew of khan Bergai of the Golden Horde converted to Christianity and became known as the monk St. Peter Tsarevich of the Horde
Full Collection of Russian Annals, St. Petersburg, 1908 and Moscow, 2001, ISBN 5-94457-011-3.