The group that gained more political participation when amendments were added to the Constitution is primarily African Americans. The 15th Amendment, ratified in 1870, aimed to secure voting rights for African American men, though it faced numerous obstacles in practice due to Jim Crow laws.
While other groups, such as Native Americans, Asian Americans, and Hispanic Americans, have also gained political rights through various legal changes over time, the most significant and direct impact from constitutional amendments in terms of broad legal recognition and protection of voting rights is associated with African Americans.