Complex sentence: The Byzantines followed, and pushed deep into Persian territory, culminating in a raid on Atropatene, but in 577, Justinian was defeated in Persian Armenia, forcing a Byzantine withdrawal.
Split into simpler sentences: The Byzantines followed, and pushed deep into Persian territory, culminating in a raid on Atropatene. In 577, however, Justinian was defeated in Persian Armenia, forcing a Byzantine withdrawal.