The group that gained more political participation with amendments to the Constitution would primarily be African Americans. Specifically, the 15th Amendment (ratified in 1870) granted African American men the right to vote. Later amendments and legislative acts, including the Voting Rights Act of 1965, further expanded and protected the voting rights of African Americans, addressing various discriminatory practices.
While other groups also gained political rights through amendments and legislation over time, African Americans are the most notable example in the context of constitutional amendments.