Izyaslav I became Grand Prince of Kievan
Russia on the death of his father
Yaroslav I in
1055. Yaroslav had tried to set up a system where his
sons would not be fighting one another for
power after his death; he gave each a
city to rule as
prince, with the eldest as Grand Prince over them all, and when the Grand Prince died, the next eldest became Grand Prince and all would move to the next city on the list. The major problem with this is that most of the princes preferred to provide for their sons than for their grown brothers, so it didn't work out at all well.
At first Izyaslav's reign did adequately. Kievan Russia was able to conquer some more surrounding tribes (the Torks and the Galindians). Some of Izyaslav's brothers died, and at first the brothers did move to a new city to replace the previous prince. But in 1064, one of Izyaslav's nephews (Rostislav Vladimirovich) managed to push his cousin (Gleb Sviatoslavich) out of the city of Tmutorokan. Gleb's father (and Izyaslav's brother) Sviatoslav marched on the city, managed to push Rostislav out, put Gleb back in as Prince, and went home. As soon as Sviatoslav was gone, Rostislav came back and threw Gleb out again. At this point, a year after the mess started, another nephew of Izyaslav (Vseslav Bryacheslavich) took advantage of the situation and marched on Novgorod. Izyaslav, Svyatoslav and their brother Vsevolod sent a joint army to Vseslav's territories in 1067. They managed to defeat him and put him in prison, but as they fought in the north, another menace was creeping up in the south.
The Polovtsi, who formerly controlled some of the tribes Izyaslav had conquered at the beginning of his reign, attacked Russia in 1068; the brothers managed to bring troops south to meet them but were defeated. The princes all fled north to their home towns; the people of Kiev demanded that their Grand Prince Izyaslav arm and lead them into battle with the Polovtsi. Izyaslav refused, whereupon the people of Kiev released Vseslav from prison and proclaimed him Prince of Kiev. Izyaslav and Vsevolod fled to Poland.
However, Svyatoslav managed to defeat the Polovtsi with his own armies, and Izyaslav came back with a Polish army to take back his throne. Vseslav fled to his home city of Polotsk, and the citizens of Kiev appealed to Svyatoslav and Vsevolod to protect them from their angry ex-prince. The brothers did manage to calm Izyaslav down a little; he sent in his eldest son to execute the ringleaders of the movement that had thrown him out, but did not take vengeance on the whole city.
Izyaslav reinstated himself as Grand Prince and sent his sons to Polotsk to be its Princes. While Izyaslav was preoccupied with yet another Polovtsi invasion in 1071, Vseslav tried unsuccessfully to retake the city. Despite this constant fighting between Izyaslav and Vseslav, the next year Sviatoslav managed to convince Vsevolod that Izyaslav was plotting with Vseslav against them. The two sent troops to Kiev, and Izyaslav fled the country again. Sviatoslav II stayed on as Grand Prince of Kiev for three years until his death in 1076, whereupon (again) Izyaslav came back with a Polish army and took back the throne rather than letting Vsevolod have it.
Vsevolod did not fight this, and became an ally of Izyaslav against some of Sviatoslav's sons and nephews who kept up his cause (including Vseslav). The two sides continued fighting for two years, and at a battle outside Chernigiv in 1078, Izyaslav was struck by a spear and killed. He was succeeded by Vsevolod.