Complex sentence: Some historians have claimed that Sergius IV was essentially a puppet ruler for Crescentius III. Others, however, claimed that the Pope resisted his power; there is some evidence that Sergius IV gave political backing to an anti-Crescentius faction in the city.
Split into simpler sentences: Some historians have claimed that Sergius IV was essentially a puppet ruler for Crescentius III. Others, however, claimed that the Pope resisted Crescentius III's power. There is some evidence that Sergius IV gave political backing to an anti-Crescentius faction in the city.