[ykler]

This is very interesting. Why was it thought that at-large districts would dilute the black vote? Blacks were a minority in every southern state, I believe, so naively one would think that they would stand to benefit from at-large districts and suffer from gerrymandering. The only way I can think this might not happen is if the plan were to only have a very small number of the representatives (like one) be at-large, but presumably the relevant proposal should be to have all representatives be elected on an at-large basis (?)

[bonyt]

This is because an at-large system isn't the same as a proportional representation system. In an at-large system, 51 percent of voters can still control 100 percent of the seats. This is because each voter gets one vote per seat. For example, if a hypothetical state had 5 Representatives elected on at at-large basis, and 51% of the state favored one party, they could win 51% of the vote for each seat, and win every seat.

[zachrose]

It may be true that no state had a Black majority in the 1960s, but several states did have a Black majority until the 20th century. From Wikipedia:

Three Southern states had populations that were majority black: Louisiana (until about 1890), South Carolina (until the 1920s) and Mississippi (from the 1830s to the 1930s).

https://en.m.wikipedia.org/wiki/Majority_minority