What was the danger of feudal fragmentation for the Russian lands?

During the period of feudal fragmentation, several principalities were formed on the territory of Russia. Each principality gradually formed its own orders, the economy was mainly natural, there was no need to form a single market, to buy something from neighbors. The danger of such a situation was that the principalities were constantly at war with each other, which weakened them. Also, there was no single army, which at that time was needed to protect against enemy raids.