Complex sentence: The Middle Ages in Dalmatia were a period of intense rivalry among neighboring powers: the waning Byzantine Empire, the Kingdom of Croatia (later in a personal union with Hungary), the Bosnian Kingdom, and the Venetian Republic.
Split into simpler sentences: The Middle Ages in Dalmatia were a period of intense rivalry between the involved factions. The waning Byzantine Empire, the Kingdom of Croatia (later in a personal union with Hungary), the Bosnian Kingdom and the Venetian Republic.