Final answer:
Rosa Parks' most important contribution to the Civil Rights Movement was sparking the Montgomery Bus Boycott through her act of nonviolent defiance, which emphasized the strength of community activism and led to the Supreme Court declaring segregated buses unconstitutional.
Step-by-step explanation:
Rosa Parks' most important contribution to the Civil Rights Movement was her act of defiance on December 1, 1955, when she refused to give her seat to a White man on a Montgomery bus. This singular act of nonviolent resistance became a pivotal moment in the Civil Rights Movement, sparking the Montgomery Bus Boycott. Parks was a respected member of the community and an active member of the NAACP, making her arrest the catalyst for change. Organized by the Women's Political Council and supported by prominent figures like Martin Luther King Jr., the Montgomery Bus Boycott demonstrated the efficacy of unity, organized nonviolent resistance, and the significant role of African American churches in the movement.
The bus boycott lasted for over a year, with African American citizens walking and finding alternative transport, showing remarkable solidarity and determination. The success of the boycott ultimately led to the Supreme Court's decision that declared segregated buses unconstitutional. Rosa Parks' courageous decision and the community's response exemplified the power of community activism and set the stage for further actions towards desegregation and equal rights.