The group that gained more political participation when amendments were added to the Constitution is primarily African Americans. The 15th Amendment, ratified in 1870, granted African American men the right to vote. Subsequent legislation and amendments, including the Voting Rights Act of 1965, further reinforced and protected their voting rights.
While other groups, including Native Americans and women (who gained suffrage through the 19th Amendment), also saw increases in political participation, African Americans are most directly associated with constitutional amendments that explicitly addressed their voting rights during the reconstruction period and beyond.