Um, you realize the union folks owned slaves also?
So the union was evil?
Slavery is evil. To own a slave is evil. To sell a slave is evil. That is my moral judgement. Yours may be different.
There are things that are more evil. Starting a war to further and extend slavery would be one of those things. The US didn’t do that. That would be the pretended confederacy that did the more evil thing.
Let me help you. The federal government had no power to regulate slavery in the various states. Accordingly, the states that permitted slavery permitted that evil, and the people of the state governments that could have ended that evil and did not missed a great chance to do good, to their great shame.
The great project of self government was diminished because some of the greatest proponents of independence were drivers of negro slaves. The presence of negro slavery was exploited by the British to hinder independence, and because of that weakness in the states, the battle against the British continued longer.