The Bell Riots were an event that took place in San Francisco on Earth in September 2024. They led to the end of the Sanctuary Districts, and marked the real beginning of Humans working to find a lasting solution that would resolve social problems. This would set humanity on the path to eventually founding the United Federation of Planets.
By the 2020s, those without employment, as well as those with mental problems, were moved into the Sanctuary Districts, which would later become no better than slums.
In August 2024, a riot began in San Francisco's Sanctuary District A, in which several workers were taken prisoner. Benjamin Sisko, posing as Gabriel Bell, helped ensure the hostages' survival. The American public was made aware of the true nature of the Sanctuary districts after Jadzia Dax convinced Christopher Brynner to use his company's Internet channel to show recordings of District inhabitants. However, the governor of California ordered the National Guard to move in and regain control, killing hundreds of the inhabitants. (DS9 episodes: "Past Tense, Part I", "Past Tense, Part II")
The outrage over the deaths of Bell and the several other Sanctuary District residents led to the districts being closed down, and the beginning of the United States of America correcting its social problems. (DS9 episode: "Past Tense, Part I")
Following Sisko's return to the 24th century, he discovered that the picture of Gabriel Bell was that of himself. The Federation Department of Temporal Investigations looked into Sisko's involvement in the Bell Riots. (DS9 episode: "Past Tense, Part II", STO novel: The Needs of the Many)
In an alternate timeline created by the death of Bell prior to the riots, Earth remained a pre-warp civilization, which never expanded beyond the Sol System, in the 24th century. Consequently, neither the Federation nor Starfleet ever existed. The USS Defiant, having been protected from the changes in the timeline by a subspace bubble, detected Romulan transmissions emanating from Alpha Centauri. This would indicate that the Romulan Star Empire was able to expand considerably further in this timeline, due to the lack of Federation interference. (DS9 episode: "Past Tense, Part I")