I tried to respond by keeping it short in time (for me). Appearantly I was too brief.
I am not an expert on the history of the theory of evolution. But I do know that Darwin did not create it. He was a leading promoter. A century before Darwin some philosophers (Voltaire? Rousseau?) pushed the theory of evolution (I assume evolutionism is an outgrowth of the Protestant Reformation). And I believe it was promoted in the French Revolution of the late 18th Century. The theory of evolution was not something new to slave owners with Darwin’s book.
The abolitionists were a curious bunch. They were not, for the most part, supporters of equal rights. They most slavery and abuse. They felt Blacks should not be educated beyond the 4th grade. Not have equal pay, not shop at white places, live in white neighborhoods or marry whites. (Walt Whitman supported equal rights). Lincoln was so radical in his views of slvery that the South started seceeding before he took office. Today his views would label him an extreme racist.
Christian denominations split over the issue of slavery. The Southern Methodists and Southern Baptists were formed to defend it.
The Kansas-Nebraska Act was set to allow those states self determination on the issue of slavery in order for them to achieve statehood. Hundreds were killed in the battles that followed (Bleeding Kansas). if they did become slave states there would have been very few slaves anyway. Arizona and New Mexico were slave territories but it is unknown if either territory had any slave. Nor are there any known in West Texas.
As stated before the secession statements of 7 states included the defense of slavery.
During the Civil War there were secret organizations, such as the Knights of the Golden Circle,who planned to expand slavery to Central America and Cuba after the South won the war.
Toward the end of the war several generals, including Robert E Lee, argued for the enlistment of Blacks. But the president of the Confederate Congress opposed the idea stating thatthere was no purpose then for the war. Enlistment did occur but it was too late for them to see combat.
After the war Nathan Bedford Forrest and the man who wrote the rule book for the Masons created the KKK (Forrest later left in what may have been a religious conversion). The KKK, as we all know, grew quite powerful throughout the South and the North. Segregation and Jim Crowe laws also existed.
A form of slavery existed well into the 1950s in the presence of chain gangs. Blacks were often convicted of crimes they did not commit and even of “crimes” that never even happened.