I've recently seen this question a lot in other subreddits. So I want to come here to get a straight answer.
The GOP was a progressive party in the 1860's extending voting rights and emancipation to otherwise disenfranchised groups. In the 1960's it was a democratic president that signed the civil rights act.
How did the republicans become the "conservative" party? Also, why do so many people say that the switch is a myth?
Not to dissuade any new comments on the matter, but you may be interested in our FAQ section on the Changing role of Republicans and Democrats.
Many call this a myth, I am inclined to believe them; however, it is understandable where the confusion comes from.
I think people are generally confused by the nineteenth century Republican Party and its policies. While the GOP, was an anti-slavery party, and it generally represent northern factories and such, it was not a 'progressive' party as we would call it. Part of this has to do with the evolution of 'liberalism' and 'conservatism' over the later half nineteenth century and earlier half of the twentieth. The GOP was not advocating for total integration of former slaves into society, and there voter base was white, upper to middle class factory owners. Sound familiar? Now many point to the 'black' support for the Republican party as one of the primary reasons for the 'switch'. I would call this nonsense, because many former slaves were uneducated, but obtained voting rights, therefore they were going to vote for the party that freed them. Another thing people point to is the Religious association. The nineteenth century and early twentieth century GOP was not as 'religiously' orientated that we perceive today. This is one of the things, like many, that has changed in the GOP over the years. At some point in the 1950s-60-70s the religious voter base started to switch from Democratic to Republican, I would infer that this switch had to do more with the Democratic adoption of desegregation to its party platform, less that a change in Republican ideology.
Now I am sure you are thinking 'wow how come you have covered the Republican Party, but nothing about the Democratic Party?' Well the democratcs are the 'oldest' singular party, and talking about their history in contrast with the Republican party is useless, I find. The democratic ideology has changed so much over such a long time that I would venture to say that you could probably split it up into three separate parties and no one would tell the difference.
However, In conclusion, I have found that the 'switch' is less about the Republican Party changing but more about the rest of the world changing around them. Leading to the Republican party to become 'conservatives'(Which is, if anything, 19th century radical).