In order from earliest to latest 20th Century, they started with an even mix of jazz, big band, and classical. By the mid-50s, most big bands had died out, and were replaced by classical rock. By the mid-60s, jazz was lesser known, and was almost completely replaced by contemporary blues. By now, classical rock was starting to conform into the rock that was known in the 70s and 80s. By the late 70s, rock, pop, and Contemporary R&B had taken over. It remained this way until the mid 90s. By then, rock had pretty much dissipated, and taking it place, rap hit the scenes. It remains the same to this day.
Hope this helps! I specialize in this kind of stuff, especially the early to mid 20th Century, so hopefully my knowledge helps... Anyway, best of luck to you. Have a great day!
