The Republican Party was founded to destroy slavery. Abraham Lincoln led that fight. 389,753 Union troops died and 275,175 were injured. Many of those Union troops were black but the vast majority were white.
After Reconstruction, the Democrats instituted segregation and enforced it with their terrorist arm, the KKK. The KKK murdered blacks and Republicans.
It was President Dwight Eisenhower who signed the first Civil Rights act in 1957.
President Johnson’s Civil Rights Act passed because of Republican support. Southern Democrats were fiercely opposed to it.
We can go into a long discussion about why blacks, well, inner city blacks, have been mired in poverty and crime. Renowned black economist Thomas Sowell is good on the subject. The biggest factor has been the disintegration of the black family. Out of wedlock births went from numbers comparable to white numbers before 1960 to over 70%. White Democrats passed welfare legislation that rewarded unmarried women and let the fathers off the hook. Incentives matter, and, in poor communities with lousy schools, and no job prospects, black communities struggled.
There is a lot that can be done to help the black community. Donald Trump is going to help them with school choice, improved job opportunities, strong law and order and strong borders.