This question originally appeared on Quora. 
By Sean Trende, Senior Elections Analyst, http://realclearpolitics.com/, co-author, Almanac of American Politics 2014
As a threshold matter, I dislike the term "realignment." As I explain in my book, The Lost Majority, that has connotations of permanence and enduring strength that I just don't see as realistic. Political coalitions come and go, sometimes quickly, sometimes slowly - and in the South, it was soooo slow that it's hard to consider it realigning.
In any event, the "realignment" of the South is such a complex, lengthy phenomenon, that I doubt we'll see it repeated any time soon. In truth, the movement of the South toward the Republicans proceeded in three steps, which are only just now being completed. 1964 is an important date, but it is at best a midpoint, not a start date. 1936,1952, and 1956 are equally important, if not more so.
Remember, while it is certainly important to examine the years where the GOP went from forty percent to fifty percent in the South, it is equally important to know why the GOP could go from twenty percent support to thirty percent support. That happened during Franklin Roosevelt's term, when the increased economic liberalism, combined with the economic rejuvenation of the South, pushed the region rightward. The *biggest* drop in Democratic performance in the South comes between 1932 and 1952, when Democratic performance fell 40 points, as opposed to 10 points in the ensuing years. Note that this was while the Democrats were still the official opposition to Civil Rights, while Republicans were still staunchly in favor of them.
This was because the South was growing. Textile plants, paper mills, and even Kraft foods were moving southward, and once-sleepy towns like Richmond, Virginia, Charlotte, North Carolina, and Atlanta, Georgia, became bustling cities. These cities also began to provide support for Republicans; when Hoover nearly carried the South in 1928, these areas played a critical role in his success. In their award-winning book The End of Southern Exceptionalism, political scientists Byron Shafer and Richard Johnston carefully document the correlation between the rise of a wealthy, urban class in the South and the rise of Southern Republicanism. Shafer and Johnston thoroughly examined of election data from 1952 through 2000 and found that, especially at the Presidential level, the earliest steps of the Southern realignment were an outgrowth of economic development.
So Step I was the growth of Southern cities and suburbs, and their movement toward the GOP. Obviously, the Civil Rights Act of 1964 did not help Southern Democrats any, and it helped precipitate Step II, which was the realignment of Wallace voters toward the GOP. Of course, this too revolved around a number of issues other than race, including the growing counterculture, the Vietnam war, and increasing domestic unrest. But race was obviously a large part of this as well.
Finally, recently, the areas of the rural South that supported Humphrey in '68 - largely populistic Jacksonian voters in the Southern highlands - have swung toward the GOP.
That it took seventy years for this to occur from the start of the Southern "realignment" is a testament to what a complex process that "realignment" was, and how difficult it will be to see anything like that again anytime soon.