Complex sentence: Before this happened, his brother Olof died, and a new co-ruler had to be appointed, but the Swedes refused to accept his rowdy nephew Styrbjörn the Strong as his co-ruler.
Split into simpler sentences: Before this happened, his brother Olof died, and a new co-ruler had to be appointed. The Swedes refused to accept his rowdy nephew Styrbjörn Starke as his co-ruler.