In what era did sound films become a mainstream form of cinema?

Sound films became a mainstream form of cinema in the late 1920s primarily due to the technological advancements that allowed synchronized sound to be effectively integrated into motion pictures. The transition from silent films to "talkies" started with significant milestones, such as the release of "The Jazz Singer" in 1927, which was the first feature-length film with synchronized dialogue. This technological breakthrough captured the public's imagination and marked a pivotal moment in film history, leading to the rapid adoption of sound across the industry.

By the late 1920s, filmmakers and studios recognized the commercial potential of sound and began to invest heavily in the production of sound films. This era saw an explosion of innovation in cinematic storytelling, with sound enhancing not just dialogue but also music and sound effects, thus changing the way stories were told and experienced in cinema.

In contrast, the other time periods mentioned did not see sound films reach their peak mainstream popularity. The late 1910s were still primarily dominated by silent films. The early 1940s marked a different phase in film history, focusing more on World War II narratives and other genres. The mid-1950s was a period of evolution with television becoming a competitor, which ultimately shifted focus again in the cinema