Post Civil War:
African Americans supported the republican party for 110 years, due to its support of African American issues and abolitionist support. And after the civil war support for the placement if African American in political positions. The democratic party however reacted violently to this support, and removed African American politicians and supporters through violence, threats, blocking polling stations and by supporting the implementation of voting retraction laws.
The work of abolitionist made fruit by the freedom of the slaves by a republican president after the war the appointment of African Americans in political positions was a huge step for equality. But this progress was largely undone by the brutal tactics by democratic party. Process was slowed further by the democratic party by the election of Andrew Johnson. Republican power was somewhat restored by the election of Ulysses S. Grant. But grant do Little for civil rights with old democrats making up a majority of house senate blocking any type of reform to better African American lives.
Woodrow Wilson didn't help - democrat. Warren G. Harding, Calvin Coolidge were both republican, but were focused on other things (women's suffrage and scandal). But not on African American issues. Even with the republican party having majority in both the senate and house during those times, not much progress in racial equality was made.
Starting in 1869 African American support for the republican party began to shift gradually to the democratic party. Most notably in the 1940s during the Roosevelt administration - democrat (thanks mostly to the war and his wife).
After, nothing notable transpired until the Eisenhower administration - republican. When the U.S. government forcefully intervened by reinforcing the Supreme court's decision on Brown v. Board of Education.
Civil Rights: African American support for the democratic party solidified during the Kennedy and Johnson administrations in the 1960s.
Most notable was the democrats support for the Civil Rights Act of 1964. Signed into law by president LBJ - democrat.
Future democrats saw this switch in voting and had an epiphany made famous by the quote by LBJ for the next 200 years. Thereafter, democratic candidates began speaking to African American issues. As a consequence, over the decades gained more and more African American loyalty, and votes.
1970 and 80s Richard Nixons 'Silent Majority', and Reagans 'Tough on Crime' initiatives
signaled the death of African American support for the Republican Party.