During the first half of the war the main point was to avoid succession meaning the breakage of states; division between north and south. His main focus in the start was avoid this, but as the war progresses he realized that slavery was the central issue. If slavery was allowed there was going to succession if it was outlawed there was going to be succession; so the only way to combat that is by fighting a war over slavery, where slavery can be outlaws constitutionally and not prohibiting succession; aka no sore losers