From a discussion on Metafilter:
“The Northern Democrat + Dixiecrat coalition was an incredibly strange one, brought on by really one fact — it was a Republican President and a Republican Congress that prosecuted and won the US Civil War, so there was *no way in hell* a southerner would be Republican. So, they were Democrats, and thus were in an uneasy but stable coalition with the Northern Democrats. Meanwhile, the GOP was run basically by NE republicans, who were conservative, but nothing like today.
“What changed? The Civil Rights Act. …
“Thus began the great mix mastering of the two parties. BOTH parties split. The GOP split SW/NE, the Democrats split S/N. The Dixiecrats, after going alone, ended up joining the SW GOP, what was left of the NE GOP slowly moved into the Democratic sphere or faded away….
“By the time Reagan came along (in national terms) the realignment was all but done. There were quite a few Southern Dems still left, but they were GOP in all but name and most of them switched parties after the 1980 election.
“Seriously. There Civil Rights era defines our politics and our lives today. The rise of suburbia is not just because of the highways being built, it was a direct reaction to the riots that happened in cities during this era, the most prominent being the 1967 Detroit Riot. The reason that even dramatically conservative black populations strongly vote Democrat is they remember who the GOP — the Dixiecrats of 1950.
“No other factor since WWII affects us more. The hatred of government? Between forced integration and busing of children to balance schools, the idea that the government wasn’t actually here to help you got set into everyone minds. The lack of school funding? People with money (primarily white) pulled their kids out of the now integrated schools, put them in private schools, then voted to cut school spending massively because they weren’t sending their kids to public schools. Reagan only tapped this with the “welfare queen” schtick he pulled. Ripping out neighborhoods for highways? Needed those to get to work if you didn’t want to live with “those people.”
“Fundamentally, the US is what it is because of racism, and the GOP is what it is because they’re all for making sure that non-whites get nothing from government.”