Complex sentence: But according to Adam of Bremen, Sweyn Forkbeard was forced to defend his Danish kingdom from attacks by Olof who claimed the Danish throne, the conflict was resolved by Sweyn's marriage with Olaf's mother and the two kings were therafter allies.
Split into simpler sentences: But according to Adam of Bremen, Sweyn Forkbeard was forced to defend his Danish kingdom from attacks by Olof who claimed the Danish throne. The conflict was resolved by Sweyn's marriage with Olaf's mother and the two kings were therafter allies.