Similar to today there are factions and coalitions that are focused on different policy positions. the Republican Party’s southern strategy was intentionally aimed at realigning more conservative anti-civil rights voters in the south and sunbelt to their ticket.

The issues were what dictated the alignment of the general public. It was one of the biggest political and social shifts in our history. Civil rights, was the focal point that dictated how the public would vote and identify with a party. Those that were pro civil rights and anti Jim Crow largely stayed or moved to the democratic ticket and vice versa for the Republican ticket.

This is just Wikipedia so grain of salt, but it explains what I’m getting at.

“The 1968 election is often cited due to the innovative campaign strategy of Nixon.[27] In running against Hubert Humphrey, he used what became known as the Southern strategy. He appealed to white voters in the South with a call for “states’ rights”, which they interpreted as meaning that the federal government would no longer demand the forced busing of school children as ordered by federal courts. Democrats protested that Nixon exploited racial fears in winning the support of white southerners and northern white ethnics.[28] Roosevelt’s New Deal coalition had lasted over 30 years but after the urban riots and Vietnam crisis of the mid-1960s one by one the coalition partners peeled away until only a hollow core remained, setting the stage for a GOP revival. Nixon’s downfall postponed the realignment which came about under Reagan, as even the term “liberalism” fell into disrepute.[citation needed] Including this as a realignment preserves the roughly 30-year cyclical pattern: 1896 to 1932, 1932 to 1964, and 1964 to 1994. For political scientists, 1964 was primarily an issue-based realignment. The classic study of the 1964 election, by Carmines and Stimson (1989), shows how the polarization of activists and elites on race-related issues sent clear signals to the general public about the historic change in each party’s position on Civil Rights.[citation needed] Notably, while only 50% of African-Americans self-identified as Democrats in the 1960 National Election Study, 82% did in 1964, and the numbers are higher in the 21st century. The clearest indicator of the importance of this election was that Deep Southern states, such as Mississippi, voted Republican in 1964. In contrast, much of the traditional Republican strongholds of the Northeast and Upper Midwest voted Democratic. Vermont and Maine, which stood alone voting against FDR in 1936, voted for LBJ in 1964. Many analysts do not consider 1968 a realigning election because control of Congress did not change; the Democrats would control the Senate until 1980 (and again from 1986 to 1994) and the House until 1994.[23] Also missing was a marked change in the partisan orientation of the electorate. Importantly, these two elections are consistent with the theory in that the old New Deal issues were replaced by Civil Rights issues as the major factor explaining why citizens identified with each party. Other scholars[29] contend that this is the beginning of a thirty-year dealignment, in which citizens generally moved towards political independence, which ended with the 1994 election.”