Resources on the 14th Amendment which established birthright citizenship, granted citizenship to all formerly enslaved individuals, and established equal protection under U.S. law, and the 15th Amendment which granted the right to vote to Black and formerly enslaved men nationally.
Resources on the Indian Citizenship Act which granted Native Americans U.S. citizenship but not full voting rights.
Resources on the Voting Rights Act and the Civil Rights era.
Resources on Shelby County v. Holder (2013), the recent Supreme Court case that struck down the Voting Rights Act.