You mean I can't ask such a question? As a European origin naturalized American citizen I know in Europe grudges ans losses in war are remembered for generations. Yet the Southern man salutes the flag of teh nation that burned down Atlanta and other Southern cities. I was only asking what caused the Southern people to overlook this? Complex question I as a transplanted into the North American can not answer - maybe even Southerners can't answer it either?
(Speaking as a northerner whose family history is steeped in the 48th Pennsylvania Volunteer Infantry, FWIW...)
The answer, as I understand it, is that Union means Union. The rebellious States weren't simply busted up and recolonized by the North; they were readmitted to the Union. What remained of the Confederacy and its culture was fully a part of the character of the Nation that resulted. It was more of a merger than a conquest.
I think Southerners now fight for the Union, as it were, because they're fighters!
In some places, there is still deep anger towards the Yankees, especially in isolated areas where the guerilla war had neighbors fighting one another. But just as the U.S. is now, and has been for over 100 years, an ally of Britain, the South may have conflicts with the north, but we're still together against the rest of the world.