Final answer:
The Civil Rights Movement most significantly increased the presence of African Americans in Congress through key legislation and activism efforts in the 1960s.
Step-by-step explanation:
The Civil Rights Movement primarily helped to increase the presence of African Americans in Congress. This movement, in the 1960s, was driven by grassroots activists and resulted in crucial legislation such as the Civil Rights Act of 1964, the Voting Rights Act of 1965, and the Civil Rights Act of 1968. These legal victories were pivotal in supporting African Americans in securing equal access to rights and privileges, which included increased political representation. Although other minority groups also fought for their rights and saw some increases in representation, the broader advancements in Congress during and after the Civil Rights Movement were most notably seen among African Americans.