The Battle Hymn of the Republic was composed to the tune of John Brown’s body because so many of the early volunteers in the Union army were bloodthirsty abolitionists who marched South singing about a murderous maniac who wanted to unleash a race war upon Virginia as if he were a saintly martyr
Such attitudes did much to harder the opinion of the South and lead even those skeptical of secession, like Robert E Lee, to fight to the end
As Fleming notes, “Could General Lee invade Virginia or any other southern state at the head of an army composed of men who believed John Brown was as divine as Jesus Christ? How would the orders of a southern-born general, a slave owner thanks to his wife, restrain such men?”
I recommend you re-listen to the Battle Hymn of the Republic, read the lyrics, and join the Glorious Cause.