The unity of Russia, restored by Yaroslav, finally disappeared after his death in 1054. Under his sons and grandsons, the Kievan Rus turned into a number of separate and independent duchies, united only by the church and the knyazes belonging to one family. The feuds between the children of Yaroslav resulted into the general decline of Rus -- both political and economical. Russia, who recently defeated Pechenegs, now suffered from attacks of another nomadic tribe, Polovs, who came into the southern steppes in mid-XI century. They occupied the eastern and soutnern trade routes and disrupted the trade. By XIII century, only 150 years after the death of Yaroslav, the Kievan state dissolved into independent entities and Kiev became an desolated town, stricken by poverty.
One of the reasons for such decline was the order of succesion established by Yaroslav. He gave Kiev and Novgorod to his elder son, Izyaslav, Chernigov to Snyatoslav, Pereyaslavl to Vsevolod, etc. The elder brother was the grand prince, but he did not rule the whole state. For the knyazes, Russia was a property of the whole their family. Every knyaz hoped to become the grand prince (velikiy knyaz) some day, when his older brothers die. The title of the velikiy knyaz was inherited not by his son, but by his younger brother. If he had no brothers, it was the elder nephew, that is the eldest son of the his eldest brother. So, when the knyaz of Kiev died, hiw brother from Chernigov had to move to Kiev, and the third brother moved from Pereyaslavl to Chernigov, etc. When a knyaz died not having reached the title of the grand prince, his children lost the right to succeed and became izgoys, who had no place in Russia.
These rules were very difficult to observe. The very first heirs of Yaroslav started fighting for the throne. Izayaslav was exiled from Kiev by Kievans themselves, and when he managed to get the throne back, he was exiled again by his brothers Svyatoslav and Vsevolod. Izyaslav left to Germany where he tried to obtain help from Henry IV and Pope Grigory VII, but to no avail. Svyatoslav ruled in Kiev till his death. Only after his death, Vsevolod allowed Izyaslav to take the throne for the third time. Vsevolod became the next ruler. So, they ruled in the following order: Izyaslav, Svyatoslav, Izyaslav, Vsevolod. Had Svyatoslav not seized Kiev, he would not become the grand prince, since he died earlier than his elder brother Izyaslav.
On this pretext, Izyaslav and Vsevolod after Svyatoslav's death decided that his children, Oleg and Yaroslav, became izgoys. This feud went on for many years and many knyazes were sent into exile or killed, until in 1097, the knyazes gathered in Lyubech, where they decided on a council that every knyaz should stay in his own knyazhestvo (duchy). Svyatopolk son of Izyaslav stayed in Kiev, children of Svyatoslav ruled Chernigov and Vladimir Monomakh, son of Vsevolod, became the knyaz of Pereyaslavl. So, sons of Svyatoslav got the rights of knyazes.
The feud did not stop after this congress. When the Grand Prince Svyatopolk died in Kiev in 1113, the Kievans refused to give the throne to the knyazes from Chernigov, but invited Vladimir Monomakh, who was respected in all parts of Russia. Vladimir refused to become the Grand Prince, but the Kievans insisted and, at last, he agreed. So, the order of succession established by knyazes was violated by the gathering of citizens.
From the above, we can see the reasons of the political disorder in Kievan Russia:
- the order of succession established by Yaroslav was too complicated and unjust;
- stronger knyazes often violated the accepted rules;
- the population sometimes refused to honor the decisions of the knyazes and elected the rulers by themselves.