The sanctimonious passing of judgment on one another, increasingly evident after 1820, and accelerating into the middle of the 19th Century, was the actual cause. The idea of tearing down the honored heroes of the Old South, today, reflects a renewal of the malady--the dearth of mutual respect;--which, ultimately, is a repudiation of the very premises of that Federation.
Note how a great Twentieth Century patriot, General Douglas MacArthur appropriately honored both "Blue & Gray":
Tolerating & respecting historic differences was the key to healing the terrible wounds of a terrible war. (Note MacArthur's father had been a General in that War, fighting for the Union side.
But the possibility of losing 3/4ths of all European trade (and potentially more) was the reason why the North could not allow the South to leave in peace.
There was simply too much money at stake.
Arthur MacArthur ended the Civil War as a brevet Colonel.