I keep hearing people erroneously suggest that Lincoln changed his motive for waging war on the South as the war progressed, from restoring the Union, to freeing the slaves. Nonsense, in his last speech, just four days before his death he said:

“We all agree that the seceded states, so called, are out of their proper practical relation with the union and that the “SOLE” object of the government, civil and military, in regard to those states, is to again get them into that proper practical relation.” 

I think it’s abundantly clear from that statement that there was never any new motivation for prosecuting the war and no moral high ground for the invaders to claim. It was always about conquest so Caesar would have his taxes or destroy the South in the process; so it could not compete with Northern industry…He got both.