Complex sentence: The Unione Nazionale's membership primary came from aristocratic and pro-monarchist Catholics in Turin, Milan, and Naples, along with members of the Black Nobility, and these groups represented over half of the signatories of the parties April 1923 manifesto.
Split into simpler sentences: The Unione Nazionale's membership primary came from aristocratic and pro-monarchist Catholics in Turin, Milan, and Naples, along with members of the Black Nobility. These groups represented over half of the signatories of the party's April 1923 manifesto.