I don't live in the US so I might be oblivious to some things that are obvious to a US citizen. I know that the Civil War was fought to end the slavery, that the North was for abolishing and the South was against. So it left me wondering, if half of a country fought for the betterment of african americans why the country, both South and North, remained so racist way into the second half of the 20th century. Isn't it logical that if I fought against someone's slavery I would also fight for that person's civil rights?
The idea that the Civil War was fought "to end slavery" is simplistic at best. The war was fought to maintain the union of states, to prevent the south from seceding. Therefore, there were plenty of people in the North who had no issue with the institution of slavery itself, but didn't want the south to secede. Most soldiers fighting for the north were indifferent with regards to slavery.
Even people who were against the institution of slavery itself could still (and usually did) hold extremely racist views. Lincoln himself said:
"I am not, nor ever have been, in favor of bringing about in any way the social and political equality of the white and black races … I am not nor ever have been in favor of making voters or jurors of Negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which I believe will forever forbid the two races from living together on terms of social and political equality. And inasmuch as they cannot so live, while they do remain together there must be a position of superior and inferior, and I as much as any other man am in favor of having the superior position assigned to the white race.”
With the vast majority of even abolitionists holding similar views to Lincoln, it is easy to see how post-Civil War society remained decidedly racist.