Equal Protection Clause
In a series of cases following the 1991 redistricting, the United States Supreme Court declared unconstitutional a number of Congressional districts in North Carolina, Georgia, and Texas. The Court declared that the districts in question were created predominantly for racial reasons and, therefore, were unconstitutional under the Equal Protection Clause of the Fourteenth Amendment. In holding the districts unconstitutional, the Court noted that bizarrely-shaped districts, and those which do not follow traditional districting principles such as geographical compactness, contiguity, and respect for communities of interest and political boundaries are unconstitutional if drawn for the purpose of favoring one racial group over another, unless the action is narrowly tailored to serve a compelling state interest.
The Supreme Court has held that complying with Section 2 of the Voting Rights Act of 1965 provides such a compelling reason to draw race-based districts in order to ensure that the voters of a racial group have a fair opportunity to elect a candidate of their choice. Other possible exceptions to accepted redistricting principles might be avoiding a violation of Section 5 of the Voting Rights Act and to remedy past discrimination.
In Gomillion v. Lightfoot, 364 U.S. 339 (1960), the United States Supreme Court held that it was unlawful to purposefully exclude African-American voters from voting districts under the Fifteenth Amendment to the United States Constitution.
 See, e.g., Shaw v. Reno, 509 U.S. 630, 113 S.Ct. 2816 (1993); Miller v. Johnson, 515 U.S. 900, 115 S.Ct. 2475 (1995); Bush v. Vera, 517 U.S. 952, 116 S.Ct. 1941 (1996).
 See, e.g., Thornburg v. Gingles, 478 U.S. 30, 106 S.Ct. 2752 (1986). Thornburg v. Gingles provides the Court’s most in-depth examination of Section 2, as amended by Congress in 1982, and yielded the so-called “Gingles test” for assessing Section 2 claims of vote dilution.