Complex sentence: Soon after takeoff, the plane crashed, killing Holly, Ritchie Valens, the Big Bopper, and the pilot, an infamous milestone in rock history known as The Day the Music Died.
Split into simpler sentences: Soon after takeoff, the plane crashed, killing Holly, Ritchie Valens, the Big Bopper, and the pilot. It was a tragic milestone in rock history known as The Day the Music Died.