Mariachi was heavily involved in cultural promotion as a way to create a unified Mexican identity after the end of the Mexican Revolution. One of these efforts was the promotion of mariachi as an international symbol of Mexican identity, first with radio and sound recordings and later with films. Mexico built a nationwide radio broadcasting network in the 1920s such as XEB and XEW, which began broadcasting mariachi music as a media production, rather than as a music for social events. This music was already being modified in part due to the advent of sound recording. For example, most son jaliscense
Mariachi problems recruiting mariachi instructors as many of these do not have required teaching credentials. For this reason, schools often hire trained musicians from outside the mariachi tradition. Many traditional mariachis are concerned that standardization will lead to fossilization and restrict improvisation. Other innovations in the United States have been the incorporation of styles of artists such as Elvis Presley, Freddy Fender and Glenn Miller, as well as the heavy-metal Mariachi band Metalachi. Another is the encouragement of female mariachis including all-female Mariachi groups such as Mariachi Mujer 2000 and Mariachi Divas de Cindy Shea. Mariachi Mujer has performed with Mexican