The cotton gin automated one aspect of processing cotton. The tractor automated the rest.
There were many black slave owners. The first slave owner in the new world was black. So slavery wasn’t a white-against-black invention. And don’t forget, slavery was a part of Union from the beginning. There were slaves under the US flag, too.
True enough. But every northern state had either instituted abolition or had a defined pathway to emancipation of slaves. Zero southern states had either of those.
Don’t know why, but the inevitable end of slavery in the South seemed to make their ruling class very uncomfortable:
https://en.wikipedia.org/wiki/The_Impending_Crisis_of_the_South