  We study the effect of mass media, modeled as an applied external field, on a
social system based on Axelrod's model for the dissemination of culture. The
numerical simulations show that the system undergoes a nonequilibrium phase
transition between an ordered phase (homogeneous culture) specified by the mass
media and a disordered (culturally fragmented) one. The critical boundary
separating these phases is calculated on the parameter space of the system,
given by the intensity of the mass media influence and the number of options
per cultural attribute. Counterintuitively, mass media can induce cultural
diversity when its intensity is above some threshold value. The nature of the
phase transition changes from continuous to discontinuous at some critical
value of the number of options.
