FM was in development in the 1930's, but was reallocated a couple of times. The current allocation of 88-108MHz was put into place in 1945. It took a long time

FM was in development in the 1930's, but was reallocated a couple of times. The current allocation of 88-108MHz was put into place in 1945. It took a long time for FM to catch on. It wasn't until the late 1970's that a majority of the listening public had an FM radio, especially youth. The pivot of youth listening from AM Top 40 to FM happened within a decade.