The POD that could do this with the least butterflies is the 1876 timeframe. Specifically if the Compromise of 1877 falls through, you might see some of the nastier and more violent preparations/actions of that period become a new variant of the Civil War, factoring in the Great Railway Strike for an enormous clusterfuck. Assuming, however, that Civil War means another situation ala 1861-5 with massed armies of conscripts from US sections thrown at each other.....that is not entirely plausible.