[Destro]

In other words because the Union was restored and Southerners were left to be more or less as they were before the Civil War any hatred of the Union that may have been held by Southerners was healed over time? That would make sense in a way because the war had political reasons over say nationalist or ethnic ones and animosities originating with politics die down as the politics shift to new issues?

If I was a foreign power the nation I want kick my ass and occupying me is the USA hands down. They fix you up after and let you be (more or less).

[Physicist]

Well, I think a more important factor was that the key issue, slavery, had been eliminated. You can argue about whether either the Union or the Confederate government went to war specifically over slavery, but for many of the people, slavery was the reason. Once that issue had been irreversibly decided, much of the passion drained out of the conflict. The northerners got their way, and so had no further motivation to oppress the southerners (many of whom were freed slaves anyway). The southerners lost their labor force, so the civilization of the Old South could never be put back again, Union or no.