What evidence is there that the 1920s was the first modern?

The 1920s is often considered the first modern decade due to significant cultural, technological, and social changes. The rise of mass media, particularly radio and cinema, transformed entertainment and information dissemination. The advent of the automobile revolutionized transportation, while the emergence of consumerism and advertising reshaped lifestyles and social norms. Additionally, the decade saw significant movements in art and literature, reflecting modernist themes that challenged traditional values.