Why did the socio-economic processes in the 11-13 centuries cause political fragmentation?

The whole point is that for a long time the cities were forced to pay tribute to Kiev. Economic and trade ties were poorly established between the cities themselves. In this connection, the separation took place at a rapid pace. Along with political reasons, large cities turned into separate political entities – principalities that fully existed independently of each other. There were also negative sides to this state of affairs. Constant wars and strife became the cause of devastation and ruin of the land.