Try watching it instead of judging.... which, considering the length in which you posted and the length of the video, you never did.
I watched it.
First, the author of that piece seems to miss that the South is the bastion of conservatism. Whether the predominate voting party's label was Democrat or Republican, it was always conservative, preferably Christian conservative, just like today. Those old time Democrats were as conservative as current Republcians, which is the point. Dems didn't leave the South and get replaced by Repubs. as the South's preferrential party changed over the decades. They just changed their party allegiance when the Democrat national party became more liberal vs. the Repub. party becoming more conservative.
And that was happening before the 1960's, but was very much on display in the 1964 presidential election. Nelson Rockefeller, the presumptive Repub. nominee in the initial stages of the GOP primary season, was undermined by a smear campaign orchestrated by the Goldwater camp...a la Rockefeller's divorce of his wife and subsequent marriage to a recent divorcee, in too quick a fashion (they had to be having an affair for her to marry him right after divorcing her husband!!) for these religious conservatives down here in the South. Why, it was scandalous, I tells ya!
Rockefeller represented the centrist/moderate/semi-liberal faction in the GOP (I believe it was referred to as the Eastern Establishment), a faction that had held sway over the party until Goldwater's nomination for the '64 election.
The cherry on top was Goldwater's condemnation of the Civil Rights Act. Yeah, he was for it before he was against it. What drove him to change his position was the so-called Commerce Clause, the public accommodations clauses. That's what drove whites down here crazy. It was one thing to say blacks had equal rights as long as whites weren't forced to share the same spaces. The CRA of 1964 made the "separate but equal" crap illegal, which southern conservatives still haven't forgiven nor forgotten. They were more than willing to entertain the CRA sans the Commerce Clause, but with it....outrageous! Whites would actually be forced to endure mixing of the races, anathema to their collective psyche and historical memory.
Stir in some "nuke N. Vietnam" rhetoric to that and you have the candidate that won 6 states in the 1964 pres. election. And quite the list, too. SC, GA, AL, MS, LA, and Goldwater's home state AZ. Notice anything peculiar about that list? A sea of blue with a particularly interesting red swath across what were the former leading Confederate states. Just odd.
Then the Voting Rights Act passed. Southern conservatives went apoplectic. It got bad enough that some "outside interlopers" came down from NY to MS to assist in voter registration drives. Didn't help that they were Jewish. Got killed. And despite everyone knowing exactly who did it, no one was ever prosecuted.
And guess who southern conservatives blamed for that "catastrophe"? Wasn't Republicans. It took away their poll taxes, literacy tests, civics/Constitution qualifying questions and gave those damned n*****s the right to vote like white people did. Yes, whites were subject to the same poll taxes, literacy and govt. tests, but poll taxes were rarely enforced on whites who voted as opposed to being collected from every black that tried to vote; the literacy test for whites, if even given, as opposed to blacks who always had to pass the test, was akin to the white being asked to read a passage from "Dick and Jane" while the black was given a passage from current molecular biology or physics.
Get the idea blacks didn't vote much before the VRA? That was by design. Creative alternative measures have been dreamed up since, but are simply a continuation of past southern conservative philosophy.
So Nixon shows up, actually a moderate, but pounces on this with the infamous Southern Strategy, and conservatives in the south begin their march to the Republican drum beat.
It's either that---that party affiliation changed over a couple of generations in the South because of what each party evolved into and their message and policies changed---or there was, in one generation, a mass exodus of "liberal" Democrats who used to live here with an equal and sudden mass influx of "conservative" Republicans that changed the political label preferred in the South. From my recollection, the latter didn't happen.