I wish I had some authoritative references for this. Hopefully somebody else can write authoritatively or correct me. Based on my readings, slavery was always a problematic aspect of America.
Even the founders debated whether to abolish slavery, but ultimately punted because they felt uniting the states was more important.
That is, it was a tough compromise.
Take a look at the book The Long March (about Lincoln). There was a several-decade long movement before 1864 to abolish slavery.
William Freehling's Road to Disunion covers the topic thoroughly. Most of the founders expected slavery to die away gradually. The idea that it should remain permanently didn't appear for another 50 years and was never universal, even in the Deep South.
The book also explores the tensions between slavery and American ideals, and the many complications the tensions produced.
Even the founders debated whether to abolish slavery, but ultimately punted because they felt uniting the states was more important.
That is, it was a tough compromise.
Take a look at the book The Long March (about Lincoln). There was a several-decade long movement before 1864 to abolish slavery.