Complex sentence: The Ink Spots were an American vocal group popular in the 1930s and 1940s that helped define the musical genre that led to rhythm and blues and rock and roll, and the subgenre doo-wop.
Split into simpler sentences: The Ink Spots, an American vocal group popular in the 1930s and 1940s. It's music led to the rhythm and blues and rock and roll musical genres, and the subgenre doo-wop.