What new innovation played a key role in forging a national mass culture in the 1920s?

Radio

There were many developments coming to the foreground in the 1920s that affected mass culture.  Automobiles, which had begun to be available in the early 1900s, became more prevalent.  Movies provided a common source of entertainment.  But the new innovation in the 1920s that had the greatest impact on the development of mass culture was radio, which brought familiar broadcasts into homes across the whole country.