Being willing to go to war over not seeing the handwriting on the wall. All the other western countries that had slavery managed to get rid of it without a war, some people were mad, but they saw the direction of the wind.
It was largely the fault of us Yankees for waiting so long for it to “die out on its own” (a popular phrase for generations). We refused to realize that slavery is as addictive as marijuana or cocaine because it gives a man unlimited power over the lives of others.
It could have been ended flat out with no more than an abortive revolt like Shay’s Rebellion at plenty of points...but probably not after Eli Whitney invented the cotton gin and certainly not by 1860. There were too many 1%ers with their entire fortunes invested in slavery, and too many of Bob Averages who loved to lord it over every poor negro they came across.