The early 20th century marked a period of dramatic change for Chicago. World War I and the 1920s brought rapid industrial expansion, drawing large numbers of African Americans from the Southern United States during the Great Migration. Between 1910 and 1930, Chicago’s Black population surged from 44,103 to 233,903, fueling the cultural phenomenon known as the Chicago Black Renaissance, which left a lasting mark on art, literature, and music. Racial tensions, however, also led to violence, including the Chicago race riot of 1919.

The Prohibition era (1919–1933) reshaped Chicago’s social and criminal landscape. The ban on alcohol production and sales gave rise to notorious gangsters such as Al Capone, Bugs Moran, Dion O’Banion, and Tony Accardo. Violent clashes between gangs culminated in events like the infamous St. Valentine’s Day Massacre of 1929, in which seven members of a rival gang were murdered.

Amid these social upheavals, Chicago also saw progressive reforms. Tenant rent strikes in 1920–1921 led to new protections for renters, including heat ordinances and the establishment of the Chicago Tenants Protective Association. In 1924, the city became home to the first American homosexual-rights organization, the Society for Human Rights, which produced the country’s first publication for homosexuals, Friendship and Freedom, though police pressure forced it to disband.

The Great Depression hit Chicago hard, especially its industrial sectors. By 1933, over half of industrial jobs were lost, with unemployment among Black and Mexican workers exceeding 40%. Labor activism intensified, as socialist and communist groups organized the unemployed and poor, culminating in events like the Memorial Day Massacre of 1937 at Republic Steel Works. The economic crisis also ended the dominance of Chicago’s Republican political machine, with the city becoming a Democratic stronghold that persists to this day.

Despite hardships, Chicago celebrated milestones and innovation. In 1933–1934, the city hosted the Century of Progress International Exposition World’s Fair, showcasing technological achievements and celebrating the city’s centennial. Tragedy struck in 1933 when Mayor Anton Cermak was fatally wounded during a failed assassination attempt on President-elect Franklin D. Roosevelt, a dramatic moment in the city’s political history.

Through migration, industry, reform, and resilience, early 20th-century Chicago emerged as a vibrant, complex metropolis, setting the stage for the transformations of the mid-20th century.