Another of its rulers was called "the Accursed Prince" for murdering his younger brothers, and he was defeated at the Alta River by its eventual greatest ruler, (*) Yaroslav the Wise.
It's not the Byzantine Empire, but The Tale of the Bygone Years recounts a siege of this state's capital by the Pechenegs. To forestall blood feuds, murderers here were made to pay 80 vira to the families of their victims. One of its rulers gave his daughter in marriage to Casimir the Restorer. One ruler of this state married Anna, the sister of Basil II. Another of its rulers was called "the Accursed Prince" for murdering his younger brothers, and he was defeated at the Alta River by its eventual greatest ruler, (*) Yaroslav the Wise. It was established when its capital was relieved from Khazar tribute by the Varangian Guard; it later converted to Orthodox Christianity. For 10 points, name this 9th to 13th century state ruled by the Rurik Dynasty, with a capital in modern-day Ukraine.
It's not the Byzantine Empire, but The Tale of the Bygone Years recounts a siege of this state's capital by the Pechenegs.
Kievan Rus [prompt on Rurik Dynasty]