Complex sentence: Vsevolod Olgovich, then Prince of Chernigov, the Cumans and his allies who were asked by Iziaslav to make his point against Viacheslav, continued their war against Yaropolk and crossed the Dnieper to loot the Kiev region.
Split into simpler sentences: Vsevolod Olgovich, then Prince of Chernigov, the Cumans and his allies who were asked by Iziaslav to make his point against Viacheslav. Continued their war against Yaropolk and crossed the Dnieper to loot the Kiev region.