Kievan Rus', similar to other medieval states did not last for long. In my opinion, the major factor in the fall of the Kievan Rus' was contributed to its political structures, in particular, the self-serving interests of princes and their internal feud. Kiev did not have a strong ruler and princes of all small states inside Rus' were not able to unite in order to defend themselves from powerful Tatars.
On might wonder, why Kievan society was unable to impose any political authority. The answers can be found in the core of its social system. For instance, the crises of the Patrimonial mentality led Kievan Rus' to complete destruction. As result, Kievan society never had a single sovereignty. The rotated system of advancement of its members created competition among princes for the desirable throne of Kiev. Also, as the members of ruling clan become more numerous, they identified themselves with regional interest rather than larger patrimony.
The major weakness of this system was lack of unity and central government. The arrogant powers altered princes to compete against one another, made them suspicious of each other, and created territorial conflicts among them. Then, they exploited and took advantage of the resulting division and discord. The Kievan Rus' splintered into many principalities and it left Rus' vulnerable to foreign attacks. This was the worst disaster for the Kievan world, the most serious problem besetting Kievan Rus'.
The Primary Chronicle also led me to believe that the explanation for the decline of Rus' can be found in the behavior of princes. The worst of them, like Sviatopolk, desired to rule so desperately that he murdered his brothers. Conflict between siblings was great and vicious because some of them could never expect in the rotated system to succeed to the throne. With...