Complex sentence: After settling in the Levant, the Ghassanids became a client state to the Eastern Roman (Byzantine) Empire and fought alongside the Byzantine Empire against the Persian Sassanids and Arab Lakhmids.
Split into simpler sentences: After settling in the Levant, the Ghassanids became a client state to the Eastern Roman (Byzantine) Empire. They fought alongside the Byzantine Empire against the Persian Sassanids and Arab Lakhmids.