Complex sentence: Harrison left Lt. Ostander (one of the two lieutenants who relieved Rea of command) in command of the fort and ordered punitive expeditions against Miami villages in Indiana and Ohio in retribution for the attack on Fort Wayne.
Split into simpler sentences: Harrison left Lt. Ostander (one of the two lieutenants who relieved Rea of command) in command of the fort. Harrison next ordered punitive expeditions against Miami villages in Indiana and Ohio in retribution for the attack on Fort Wayne.