 Complete the following phrase:  The most prominent struggle for power was the conflict that erupted after the death of Yaroslav the Wise. The rival Principality of Polotsk was contesting the power of the Grand Prince by occupying Novgorod, while Rostislav Vladimirovich was fighting for the Black Sea port of Tmutarakan belonging to Chernihiv. Three of Yaroslavs sons that first allied together found themselves fighting each other especially after their defeat to the Cuman forces in 1068 at the 