At the time, literacy tests, poll taxes and other hurdles to voting kept African Americans away from the ballot box. And because the Republican Party was such a small percentage of the overall electorate in the South, general elections mattered far less than primaries; the winner of a primary was virtually guaranteed to win the general election. “The Democratic Party had a monopoly on politics in the region,” said Merle Black, a political scientist at Emory University. “After blacks were eliminated as voters in the South, that ended the Republican Party.” The African American voters who did remain on the voter rolls were energized in the years following the Civil War, said Cal Jillson, a professor at Southern Methodist University in Texas. Democrats, who used to nominate candidates in conventions, began to move to primaries and runoffs as a way to unite the factions that split the party, and thus to head into a general election with an advantage against Republicans.
Today, Mississippi is one of seven states — Alabama, Arkansas, Georgia, Oklahoma, South Carolina and Texas are the other six — that require a runoff election if no candidate receives an absolute majority in a primary election. "