You presume that the old democrats are the same as the modern democrats, therefore The democrats are to blame for all the sins and republicans are saints. It is not so simple as that.
This is historically ignorant.
The southern democrats who favored segregation famously abandoned the Democratic Party enmass and became Republicans over the issue of Civil Rights,
Civil rights were championed by democratic politicians President Jack Kennedy and President Lyndon Johnson. (inconvenient that)
https://en.wikipedia.org/wiki/Southern_Democrats
One famous example is
https://en.wikipedia.org/wiki/Jesse_Helms
This is how the old Democratic south became Republican.
There used to be progressive and conservative wings in both parties, they realigned so that the Republican is mostly conservative, and the Democratic party became mostly liberal.
Some of this was a deliberate strategy
https://en.wikipedia.org/wiki/Southern_strategy
see also
https://en.wikipedia.org/wiki/Dixiecrat
All those folks (and their descendants) you blame for the evils you decry eventually became Republicans in modern times.
Southern Democrats are members of the U.S. Democratic Party who reside in the South.
Lol, okay, man that's... lol
Okay, seriously though... Just a few thoughts here and there....
In the 1850s they defended slavery in the United States
And they currently do except it's illegal immigrants and "Who's going to harvest fields or build houses or be maids and cleaning services for cheap?" I can't think of a single republican who has uttered something even close. All the republicans I know would gladly pay more if it meant that those jobs go to legal citizens. I know I would and I consider myself a common sense person that sits pretty much in the middle of everything.
with effectively all members returning to the Democratic Party
This is just a reversal of the previous platform switch with, as we commonly see, an outburst or fit because they're not getting what they want instead of sticking it out. It effectively means nothing, overall. Furthermore, saying that this makes the republican party what it is today discounts all people who's views did not switch and largely ignores the democrats coming and then going. These other people, they started republican, they stayed republican. This reversal switch is nothing more than an "I'm angry that I didn't get what I wanted" which is extremely childish.
Helms was the longest-serving popularly elected Senator in North Carolina's history. He was widely credited with shifting the one-party state into a competitive two-party state
Doesn't seem like that exactly fits what I think you're trying to prove. It brought democrats is, thereby influencing policy and perceptions.
He fought what he considered to be liberalism whenever it was on the agenda, opposing civil rights at first,
Again, doesn't support your point, I think, as he is (was) a modern democrat who gained support in the republican party (kind of like Trump as he is more like an older style democrat than a current republican). So, and I'm trying to agree with you, I see a democrat who sat in on another party and was opposed to civil rights. I'd like to agree with you on Helms here because I feel your point needs a fair shake but I can't after reading that.
Although the phrase "Southern strategy" is often attributed to Nixon's political strategist Kevin Phillips, he did not originate it but popularized it. In an interview included in a 1970 New York Times article
So, let's go with your assertion that republicans in the south were overrun and commandeered by 1950s and 1960s era democrats. Well that really means that "southern strategy" is only a democrat party ideal. Now I'm not saying republicans didn't adopt it but I am saying that in sufficient numbers, these displaced democrats can influence the way things go. That's the purpose of first-past-the-post style voting. Furthermore, if you're familiar with Dungeons and Dragons or "world building", there is a widely accepted and often researched idea that "As go the leader, so to go the citizens." That is to say that if you have an evil leader, you will see citizenry shift towards evil (and we see that being researched outside of the gaming community and applied to anthropology, history, etc) And vice versa. So if the leadership was overrun by democrats fleeing because they didn't get what they wanted and did so in sufficient numbers, they merely influenced the voter base rather than took it as it was.
And while that seems like I'm agreeing with you, I am not. That is merely because the republican party is separate in the south from republican leadership in a way that is distinct from the entirety of the rest of the country. That is due partially to rural distance and partially to tradition. Rural distance increases tradition but rural distance decreases the effect of the citizens on the leadership. And when enough of these leaders get together, they don't need party or citizen votes to do things. Take the current state of affairs of NC. Cooper is hamstrung because McRory implemented a panel which basically gets to vote on what McRory can do. The panel is 100% (or close) republican. Every citizen I've talked to, while they may not agree with Cooper and might be glad his policies don't go through, all agree that was McRory did was wrong. They recognize that when the parties switch, a republican leader may well be blocked by a democrat party panel. No citizen voted this in and the majority disagree but it was the numbers of leaders that approved this that made that change. So to with a large influx of democrat leaders. They were angry and anger stirs emotions in others. And, as Ben Shapiro rightly points out, emotions win you votes, not logic, not sense.
The States' Rights Democratic Party (usually called the Dixiecrats) was a short-lived segregationist political party in the United States. It originated in 1948 as a breakaway faction of the Democratic Party determined to protect states' rights to legislate racial segregation from what its members regarded as an oppressive federal government.
Was. That's kind of important. Furthermore, their stance would have been strongly in favor of a broad interpretation of the 10th amendment.
The party did not run local or state candidates, and after the 1948 election its leaders generally returned to the Democratic Party
Oh, so almost completely irrelevant for the discussion at hand even though it was quite an interesting read.
So, to summarize, most of your ... sources... that supposedly influenced modern republicans went back to the democratic party. Eh, I'm not convinced that you made your point. You didn't do a bad job but I don't think you proved yourself.
love your cheery picking to avoid the big picture and the broad historical facts.
Why is the south mostly republican when it used to be mostly democratic?
Last I heard, Madison Square Garden is not in the south:
https://www.youtube.com/watch?v=WpaYQqzFouw
http://armored-column.com/the-democratic-klanbake-1924/
Every racist law, without exception, was passed by democratic leaders. This includes the Jim Crow Laws. https://en.wikipedia.org/wiki/Jim_Crow_laws
And while that was indeed in the southern states, the current political climate of the south is currently overwhelmingly republican.
Let's not forget the the communist scare in the 50s (which led to "In God We Trust" on the US currency) included radical leftism.
https://en.wikipedia.org/wiki/Red_Scare
Furthermore, the NRA set up a charter in one specific city to encourage the practice of 2nd Amendment rights by black citizens in order to protect themselves from the KKK
https://the-orbit.net/blackskeptics/2012/12/20/the-nra-the-kkk-and-the-2nd-amendments-black-history/
Although that was in 1958 and 1960, it was during the aforementioned communist/radical leftism scare. Noting, of course, that North Carolina voted blue 1960: https://en.wikipedia.org/wiki/Politics_of_North_Carolina
It's the current educational and societal trend to conflate and displace the history of the democratic party in the south with the current climate today.