Complex sentence: Towards the end of this period Venice has accumulated a large and powerful fleet, although still nominally a vassal of the Byzantine Empire, Venice was increasingly independent and a rival of Byzantine for primacy in the Eastern Mediterranean.
Split into simpler sentences: Towards the end of this period Venice had accumulated a large and powerful fleet. Although still nominally a vassal of the Byzantine Empire, Venice was increasingly independent and a rival of Byzantine for primacy in the Eastern Mediterranean.