Complex sentence: After the late 1970s, progressive rock fragmented in numerous forms; some bands achieved commercial success well into the 1980s, albeit with changed lineups and more compact song structures, and some crossed into symphonic pop, arena rock, or new wave.
Split into simpler sentences: After the late 1970s, progressive rock fragmented in numerous forms. Some bands achieved commercial success well into the 1980s (albeit with changed lineups and more compact song structures) or crossed into symphonic pop, arena rock, or new wave.