Complex sentence: Commoners made up the vast majority of the Roman electorate; but their votes were worth far less than those of higher rank, and they had limited influence on politics unless barraking or voting "en masse" or through representation by their tribunes.
Split into simpler sentences: Commoners made up the vast majority of the Roman electorate; the votes of the poorest were worth far less than those of the wealthiest. Commoners in general had limited influence on politics unless barraking or voting "en masse", or through representation by their tribunes.