Крепостное право - важнейшая татаро-монгольсакя скрепа

[timelets]

In "Why nations fail" Acemoglu and Robinson talk about the opposing paths Western and Eastern Europe took with regard to serfdom. If I remember it correctly, they describe it as a critical junction but don't go much into the whys vs hows. It's quite possible that the Mongol rule played an important role in setting up the junction. For example, in "The Chosen Few" Botticini and Eckstein describe the impact the Mongols had on Mesopotamia:

Until roughly the 1290s, the Mongol Khans imposed their nomadic way of living in the newly conquered areas. They also imposed heavy taxes and demanded substantial tributes. As the number of insolvent farmers grew, many became slaves of the soil—a position previously unheard of in the Islamic world, which regarded farmers and land laborers as freemen. Some 50–90 percent of the villages in the major provinces of Persia and Mesopo- tamia were abandoned, and, according to the detailed account in the chronicles of Rashiduddin Fazlullah, only a tenth of the soil in Persia remained cultivated.

Note the social transition for the farmer from being a freeman to becoming a "slave of the soil." It's quite probable that a similar transition happened in Russia in the period from the 13th to 15th centuries. Serfdom ("slave of the soil") became the norm that persisted even after the Mongols had left. Western Europe managed to escape the Mongols and maybe that was the reason why serfs eventually became freeman there. Just a guess.