The pivotal moment in the life of Rosa Parks that led to her activism was her refusal to give up her seat to a white passenger on a Montgomery bus on December 1, 1955. This act of defiance became a significant event in the American civil rights movement, sparking the Montgomery Bus Boycott. Parks’ courageous stand challenged the unjust segregation laws of the time and positioned her as a symbol of resistance, inspiring countless others to advocate for equality and justice.