Adding one or more majority-minority districts is a historical remedy imposed by the courts. When a former Confederate state's white majority pulled all the stops to suppress black voters, the courts got more aggressive in crafting remedies.
Generally, that would be the most severe remedy imposed by a court in a voting rights case. You must add a majority-minority district > you must not eliminate a majority-minority district > you must redo your maps.
VRA section 2:
(a)
No voting qualification or prerequisite to voting or standard, practice, or procedure shall be imposed or applied by any State or political subdivision in a manner which results in a denial or abridgement of the right of any citizen of the United States to vote on account of race or color, or in contravention of the guarantees set forth in section 10303(f)(2) of this title, as provided in subsection (b).
(b)
A violation of subsection (a) is established if, based on the totality of circumstances, it is shown that the political processes leading to nomination or election in the State or political subdivision are not equally open to participation by members of a class of citizens protected by subsection (a) in that its members have less opportunity than other members of the electorate to participate in the political process and to elect representatives of their choice. The extent to which members of a protected class have been elected to office in the State or political subdivision is one circumstance which may be considered: Provided, That nothing in this section establishes a right to have members of a protected class elected in numbers equal to their proportion in the population.
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I think the reason majority-minority districts were such a prominent issue is the "and to elect representatives of their choice" language. Early on, courts just presumed that black voters would want to elect black representatives - and that they would be more likely to vote for one. A majority-minority district is an almost automatic result of those presumptions - and the logical extreme of those presumptions (% race reps = % race voters) is expressly disclaimed by the last sentence.
This case didn't go so far as to ban the creation or maintenance of majority-minority districts, but it made it much harder for lower courts to impose them.
Oh, and as a practical matter, the effects of this decision are likely a good thing for the Democrats, whose likely voters were being packed into majority-minority districts. That is, in the gerrymandering sense, packing voters into a district dilutes their voting power (the inverse of 'cracking', where the gerrymanderer splits up voters into several districts where they are individually outnumbered)
