Complex sentence: From an autocracy in Carolingian times the title devolved into an elected monarchy chosen by the Prince-electors, but until the Reformation the emperor elect ("imperator electus") was required to be crowned by the Pope before assuming the imperial title.
Split into simpler sentences: From an autocracy in Carolingian times the title evolved into an elected monarchy chosen by the Prince-electors. Until the Reformation the emperor elect ("imperator electus") was required to be crowned by the Pope before assuming the imperial title.