So you are saying that the United States, making slavery permanent and protected by the US Constitution, would have "kept the peace"?
That is an awesome example of cognitive dissonance.
I don't see how protecting slavery in the USA would "keep the peace." John Brown begs to disagree.
But what I do see is that people claiming to be against slavery, yet voting in favor of making slavery stronger legally, are lying hypocrites who do not really care about slavery.
OK Mr. Magoo...