Congress played a significant role in expanding rights to marginalized Americans during the 20th century. Here are a few examples.
1) 19th amendment- This constitutional amendment gave women in the United States the right to vote.
2) Civil Rights Act 1964- This law ended segregation in public places. This included movie theaters, restaurants, parks, etc.
3) Voting Rights Act of 1965- This law got rid of poll taxes, grandfather clauses, and literacy tests. During the late 19th and early 20th century, all of these were used as a means to prevent African-American citizens from voting. Thanks to the Voting Rights Act of 1965, all of these types of obstacles to stop African-Americans from voting were now illegal.