Complex sentence: Yoshisada launched his campaign but Akamatsu Norimura who sided with Ashikaga clan forced the Imperial force into a protracted siege by defending Shirohata Castle in Harima Province, which gave Ashikaga clan time to regroup and consolidate Kyushu forces by winning the Battle of Tatarahama.
Split into simpler sentences: Yoshisada launched his campaign but Akamatsu Norimura who sided with Ashikaga clan forced the Imperial force into a protracted siege by defending Shirohata Castle in Harima Province. This gave Ashikaga clan time to regroup and consolidate Kyushu forces by winning the Battle of Tatarahama.