Complex sentence: Historically, this included cities such as Rome, Athens, Carthage, and the Italian city-states during the Renaissance--but today only a handful of sovereign city-states exist, with some disagreement as to which are city-states.
Split into simpler sentences: Historically, this included cities such as Rome, Athens, Carthage, and the Italian city-states during the Renaissance. Today only a handful of sovereign city-states exist, with some disagreement as to which are city-states.