Complex sentence: Magnus sought to re-establish Norwegian influence around the Irish Sea, and attempted to install his own vassal king Ingemund in the Southern Isles in 1097, who was quickly killed in a revolt.
Split into simpler sentences: Magnus sought to re-establish Norwegian influence around the Irish Sea. He attempted to install his own vassal king Ingemund in the Southern Isles in 1097, but he was soon killed in a revolt.