The U.S. Constitution states nothing about political parties and George Washington hoped that political "factions" would not be a part of our federal system. The Republican Party was born shortly before the Civil War as the party of Lincoln although he ran with Democrat Andrew Johnson. Many southerners adopted the Democratic Party to deprive rights of the newly freed slaves. As a push-back against Reconstruction, the party used "state's rights" especially in passing Jim Crow Laws protecting white political and social domination. The Republican Party became complicit in allowing the Blacks to become second-class citizens as the result of the disputed election of 1876.
The Democratic Party adopted the first civil rights plank as part of its platform in 1948 after President Truman desegregated the armed services. Truman acted after a Black veteran was beaten by a police chief in South Carolina. The "Solid South" had been Democratic as the result of southern Democrat's efforts to rob Blacks of civil rights. Literacy tests, poll taxes, grandfather clauses, and terror were used to keep Blacks from voting. Republicans began to make political gains in the South by supporting states' rights arguments against the Civil Rights Act 1964, Voting Rights Act 1965, and the Fair Housing Act 1968, which were all passed during the Lyndon Johnson administration. The Civil Rights Act of 64 outlawed discrimination in public accommodations, transportation, restaurants, movie theaters, etc. Before passage, many Jefferson city restaurants posted: "We reserve the right to refuse service to anyone." Forget about eating here if you are Black. The Capital Theater roped off an area restricting Black viewers. The Voting Rights Act prohibited any state or locality to pass any law limiting voting rights of minorities. Since the Shelby decision of 2013 many states, including Missouri, have passed new laws to limit voting. The Fair Housing Act prohibits discrimination in the sale and rental of housing on account of race, religion, national origin, or people with disabilities.
The Republican Party adopted the "Southern Strategy" which supported states' rights arguments to fight against these laws. Barry Goldwater, Republican candidate in 1964, opposed the Civil Rights Act because he stated it interfered with states' rights and private business. Southern white conservatives switched their party affiliations en masse. The belief that the Republican Party in the South supported White Supremacy has made it difficult for it to attract Black voters.