What, do you think the abolitionists, many of which were Republican Congressmen in Washington, would have set on their thumbs and let the Union keep slaves?
The abolitionists were the ones running that train in the North. Lincoln himself understood that when he met Harriet Beecher Stowe and said, “”So you’re the little woman who wrote the book that made this great war.”
Like it or not, there was a large group of people, all Republican, who were not going to let that issue go away.
Northern units marched to the war singing “John Brown’s body”. Col Chamberlain wrote letters to his wife talking about their duty to rid the country of the evil of slavery. There were a lot of people who were doing what they were doing because of slavery.
There is literally not a D@mn thing they could have done about it. I've ran the math.
It takes 3/4ths of a majority of states to pass a constitutional amendment. If the 11 states that became the confederacy voted as a block, you would have to have 33 other states to override their veto. That couldn't have happened until 1895 when Utah became the 45th state. (West Virginia wouldn't have been a state if the 11 confederate states had remained in the union.)
If the 5 slave states that remained in the Union during the Civil War voted with the 11 states that became the confederacy, it would require a Union with 66 states in it to override the veto of this coalition of slave states.
So how would the abolitionists do anything about slavery? It was mathematically impossible.
There were a lot of people who were doing what they were doing because of slavery.
There were a few. Most were doing what they were doing because they were drafted and forced into a confrontation with Confederate guns against their will. Irish were grabbed right off the boat and drafted into the Union army.
For an organization that sought to stop involuntary servitude, they sure engaged in a lot of involuntary servitude.
The worst riots in US history were the New York riots of 1863. They were rioting against being forced to join the army to fight people with whom they had no quarrel, all because Abe Lincoln's government demanded it.
They resented the fact that rich people could get out of the draft by paying $300.00, which was a sum none of them could hope to produce. Funny how the wealthy and powerful men of New York weren't required to fight for the cause that benefited them the most.
Since a slave at that time in history cost about $1,000.00, the rioters chanted that "Our lives are worth less than a slave!" A Northern man's freedom could be bought for $300.00, but a slave's could be bought for a $1,000.00.
Yes, there were people who volunteered to "free the slaves", but for the most part these were "kooks". Liberals not unlike our modern "LGBT" or Abortion advocates. The majority of men of the north did not give a sh*t about the slaves, and really didn't want to fight at all. Many of them realized they were being forced to their deaths, and they did not want to do it.
You should read some of the letters written by Union soldiers just before "Cold Harbor." They sewed their names into their clothes so that their bodies could be identified after they died.