Complex sentence: During the 10th century, there were dynastic conflicts in Scotland between two rival lines of royalty; one descended from Causantín mac Cináeda (Constantine I, reigned 862-877), the other from his brother Áed mac Cináeda (reigned 877-878).
Split into simpler sentences: During the 10th century, there were dynastic conflicts in Scotland between two rival lines of royalty. One descended from Causantín mac Cináeda (Constantine I, reigned 862-877), the other from his brother Áed mac Cináeda (reigned 877-878).