Aside from gerrymandering, you should look at other historic methods of voter suppression. As example, you should look up the 1965 alabama literacy test. Black people were given tests filled with trick questions and when they failed the test, they would be disqualified from voting.

https://en.wikipedia.org/wiki/Literacy_test

The more contemporary example of voter suppression is Voter ID Laws. The United States does not issue Photo IDs to every citizen. The main photo ID system that the United States has is Driver's License. Driver's License. Driver's Licenses were not intended to be a photo ID system and some states require people to have proof of insurance to even get a driver's license.

Several states have passed Voter Photo ID laws. People who will be disenfranchised by Voter ID laws are people who cannot afford to drive or acquire other photo ID and people who have been historically disenfranchised by race.

The purpose of these laws is to disenfranchise people in the same way that literacy tests did. The purpose of the law is to create an arbitrary system for polling station to block voters. The purpose is to give the polling station permission to say "I think your ID is fake" or "I think you stole someone else's ID".

https://en.wikipedia.org/wiki/Voter_identification_laws_in_the_United_States