Complex sentence: Lepidus gained wealth and power by politically allying himself with Lucius Cornelius Sulla, but once the dictator had resigned in 79 BC, Lepidus attempted to undermine the Sullan constitution.
Split into simpler sentences: Lepidus gained wealth and power by politically allying himself with Lucius Cornelius Sulla. Once the dictator had resigned in 79 BC, Lepidus attempted to undermine the Sullan constitution.