Poor whites before the War were the lowest of the low as even GWTW amply shows. They had few political rights as Slaver control was complete. Most could not even vote. Illiteracy high educational opportunities low to non-existent. Both crippled the war effort. Prior to the time in the 1890s you speak of a Reign of Terror had taken place against Blacks attempting to maintain their political rights. Political meetings in cities like New Orleans and Memphis attacked and attendees killed.
I don't particularly care whether the principle sources of oppression came from the CSA soldiers or their officers at different times.
Republicans did indeed care about Blacks and it was ONLY they who protected them as the Democrats tried (North and South) to allow their rights be taken from them. Lincoln's death was a severe blow against common people Black or White.
I agree with you regarding Lincoln's death, because Lincoln was going to carry out the "malice toward none" program, which was basically, do nothing to try and upset the Southern social order. That would have been the best thing for the South, and as his dutiful successor, Andrew Johnson tried to carry out Lincoln's program, and how did the Radicals in Congress reward Johnson for doing what Lincoln would have wanted. If I recall right, he was impeached. All to serve the ego of Thaddeus Stevens.