It was during the 1960s, the Republican party employed the "Southern strategy" of appealing to the pro-segregationist Democrats of the American South as the Democratic party started to support the Civil Rights movement.

Part of the reason for the Democratic party supporting the Civil Rights movement was Cold War competition with the Soviet Union. The hypocrisy of the US treatment of its African American citizens was a popular subject in Soviet propaganda.

This happened over a long period of time that really started after 1915. You had the big boll weevil infestation in the south and Black sharecroppers, people tired of the constant violence and intimidation, economic refugees, etc strated to immigrate to northern cities. The GOP in the northern cities was a lot like the financial wing of the GOP today, with a concentration on small business owners, big corps, low tax policy. B/c of that they didn't really have any institutional infrastructure to integrate Black voters into their political machinery. But the Dems, even though being still racist, did know how to organize the laboring class. So you start to get this uncomfortable alliance of both groups saying, we don't really trust each other, but if you help us, we'll help you. A famous example of the uneasiness of the relationship is Chicago, where the Black voters supported Daley even knowing he had participated in the race riot of 1919 during the Red Summer.

There were set backs to this relationship, Wilson's presidency was an example. The party leadership had to balance the conservative racism of the southern wing of the party, the labor jealousy and racism of the northern party, and the needs of big city political machines in the north.

But during FDR's presidency the Black voting community became more important and FDR was forced to grant more benefits, like guarantees of jobs for Black people in war department jobs. But he still maintained segregation in the military and federal government, and imposed segregation on federal military contractors in housing, to placate southern democrats.

As Black Americans in the south saw the help their northern kind were getting, they started to align the alternative political structures they had with the national Dem party. And they got more results, like Truman's integration of the military.

By the end of Truman's term a combination of the contradiction of fighting the Nazis for freedom while maintaining Jim Crow, the political use Communists made of Jim Crow, and the valor of Black servicemen in Korea made it pretty clear that Jim Crow was immoral. If the north was forced to face the issue they would usually do the right thing. So, the Supreme Court, even the Eisenhower justices, started to swing towards the new norm.

JFK had campaigned with civil rights as part of his platform. As civil rights activists started their bussing campaign, violence broke out across the south. This was all captured on Television and broadcast the south's brutal and savage racism to televisions across the north. This forced Kennedy to move closer and closer to the civil rights movement. He was not particularly good at it and it was awkward with lots of missteps, but that's the direction he was pulled in (Tom Ricks has a new book, Waging The Good War, out that should be easy to find that gets into how the Kennedy brothers were used to leading and very uncomfortable not being in control of the movement. JFK didn't have time to learn and adjust but RFK did. https://www.theguardian.com/books/2022/oct/08/thomas-e-ricks-civil-rights-january-6-waging-a-good-war-book-military-history)

During LBJ's term, the need for the civil rights act was pretty obvious. The civil rights activists used a couple new strategies. One was having white college volunteers come down to the south to work with them and the other was to involve children (high school aged) in their activism. While a lot of Americans could look away as Black people were brutalized, it was impossible for them to ignore attacks on children and young white Americans. LBJ was able to get several civil rights bills passed.

And that's when the break gets dramatic. There were still prominent Black republicans like Jackie Robinson who wanted to work with the party. But Barry Goldwater sensed an opportunity. He started claiming that segregation was a "states' rights" issue. He refused to condemn groups like the Ku Klux Klan that showed up at his rallies. He moved GOP primaries (illegally) into segregated venues to keep out Black Republicans, and opposed the civil rights laws and court decisions ending segregation. He turned the GOP convention into a near race riot that drove out even the most dedicated Black Republicans.

Goldwater failed, the violence and barbarism was too much for people. The Alabama murder of 4 little girls at church was too much for people who considered themselves civilized and Christian to tolerate and Goldwater failed to respond. The parties really changed at that point. Southern Dems switched, they had already started leaving the party with the Dixiecrats, but now went over to the GOP. Nixon formalized it into the Southern Strategy and the election of Reagan and his dog whistles made it clear to Black voters where the GOP stood. The GOP was able to gain influence among white working classes in the North and the west by playing into this racism too. A lot of Nixon's support and the organizing for the future GOP came from California housewives in places like Orange county that were worried about integrating schools in S. California which had seen a big increase of Black people who moved to California for the war industry jobs. The best book on covering the whole topic I know of is Joshua Farrington's Black Republicans and the Transformation of the GOP. You can hear an interview with him on The New Books Network.

https://newbooksnetwork.com/joshua-d-farrington-black-republicans-and-the-transformation-of-the-gop-u-pennsylvania-press-2016

A couple good books on how the GOP picked up northern working class White people by playing to racial anxieties is Nick Buccola's The Fire Is Upon Us about William F. Buckley and James Baldwin. Buckley's campaign for mayor of NYC. https://www.nytimes.com/2019/10/18/books/review/the-fire-is-upon-us-nicholas-buccola.html

and Ralph James's Northern Protest about MLK's failed Chicago campaign. It's out of print but still relatively easy to get from a library or through ILL. Rick's book touches a little on it and ties it together with the failed campaign in XX.

Michelle Nickerson's book, The Mothers of Conservatism, is a good book on the political organizing women did for the GOP in places like Orange County. You can hear an interview with her on The New Books Network: https://newbooksnetwork.com/michelle-nickerson-mothers-of-conservatism-women-and-the-postwar-right-princeton-up-2012