A quick and largely painless Civil War where the Union curb-stomps the South in a few months, or a long drawn-out conflict that lasts longer than IOTL and causes much more damage?
Given that the Emancipation Proclamation was not issued until late 1862, it would have to be the latter option. A quick Union victory presumably would have preserved the status quo and a Confederate victory obviously isn't good for them.
Basically for Reconstruction to work for blacks in the 1860s Northern whites need to hate Southern ones with a passion. They need to want to screw them over instead of having reconciliation. A longer, nastier war will set more things in place for that type of outcome.
Assassinate enough northern politicians to make the Radical Republicans more radical and you can probably get state death theory accepted in Washington. Get that accepted and the Republicans will start craving Republican strongholds out of the South. Get that to happen and Black Americans will get a state in the Mississippi River Delta with like a 90 percent black population, far too black for the redeemers to well redeem. Americans were far to racist for black and white to live in peace and harmony back then. The best case scenario for Black Americans was to get a state. To get a least one place that didn't have Jim Crow.The fundamental problem with Reconstruction was that most Northerners were racist themselves and really didn't care much for the rights of black people, once they had been given freedom from slavery. They had little enthusiasm for a long military occupation of the South to enforce the rights of people they deemed inferior. I don't think that can easily be changed just by making the war longer.
Given that the Emancipation Proclamation was not issued until late 1862, it would have to be the latter option. A quick Union victory presumably would have preserved the status quo and a Confederate victory obviously isn't good for them.
It's entirely possible that, if the conflict is too quick, slavery doesn't even get abolished.
If the war is too long though, couldn't everybody get so tired of fighting that they agree to status quo ante bellum? There is a point where exhaustion overrides recuperation of losses.
Unlikely. The whole reason the South broke away was because the Lincoln administration would have been the final nail in the coffin of slavery. Having the union curb-stomp the rebels early on would probably go a long way to convincing people that resistance is futile.