Complex sentence: The battle of Grathe (Grey) Heath on (23. October) 1157 marked the end of a civil war between Sweyn III, Canute V and Valdemar I the Great, all contenders for the Danish throne.
Split into simpler sentences: The battle of Grathe (Grey) Heath on 23. October 1157 marked the end of a civil war between Sweyn III, Canute V and Valdemar I the Great, all contenders for the Danish throne.