The event that served as a turning point in U.S. civil rights history was the Montgomery Bus Boycott in 1955-1956. Sparked by Rosa Parks' refusal to give up her bus seat to a white passenger, the boycott marked the beginning of a mass movement against racial segregation in the South. It lasted over a year and was marked by organized protests led by figures like Martin Luther King Jr. The boycott successfully ended segregation on public buses and galvanized the Civil Rights Movement, inspiring further actions and legislation aimed at achieving equality for African Americans in the U.S.