Complex sentence: In 637 A.D Muslim army under Abu Ubaida ibn al-Jarrah captured Baalbek after defeating the Byzantine army at Battle of Yarmouk, it was still an opulent city and yielded rich plunderings.
Split into simpler sentences: In 637 A.D., the Muslim army under Abu Ubaida ibn al-Jarrah captured Baalbek after defeating the Byzantine army at Battle of Yarmouk. It was still an opulent city and yielded rich plunderings.