The US House of Representatives elects only one member from each district. Such a system can potentially make it quite hard for minority groups to gain representation. For instance, if African Americans are spread out throughout a state, they might not have sufficient numbers in any one district to elect any representatives at all.
In the past, many US states have brought about this outcome deliberately, drawing their maps to ensure whites would win every district. That’s a process known as racial gerrymandering.
The federal government addressed this in the Voting Rights Act of 1965, which made it illegal to draw districts that intentionally dilute the voting power of a protected minority. When the courts have assessed whether certain maps do this, they tend to judge the districts by “compactness.” In other words, judges assess how geographically logical the districts are, to make sure they aren’t unnaturally designed to disenfranchise minority voters.
It’s also possible to racially gerrymander to benefit minority groups, by drawing districts in unusual ways to ensure certain racial minority groups make up a majority there. Groups such as the NAACP advocate for more minority representation in Congress, and in the past, they’ve pushed for more majority-minority districts as a way to achieve that goal.
But the courts have been skeptical of this too. In a series of 1990s decisions, including Shaw v. Reno, Miller v. Johnson, and Bush v. Vera, the Supreme Court struck down certain majority-minority districts because their shapes were so “irregular” or “bizarre” that they could only have been drawn for racial reasons.