"Ideas made the opposite impact in the Confederacy. Ideological contradictions afflicted the slave system even before the war began. John Brown knew the masters secretly feared their slaves might revolt, even as they assured abolitionists that slaves really liked slavery. One reason his Harpers Ferry raid prompted such an outcry in the South was that slave owners feared their slaves might join him. Yet their condemnations of Brown and the 'Black Republicans' who financed him did not persuade Northern moderates but only pushed them toward the abolitionist camp. After all, if Brown was truly dangerous, as slave owners claimed, then slavery was truly unjust. Happy slaves would never revolt... White Southerners founded the Confederacy on the ideology of white supremacy. Confederate soldiers on their way to Antietam and Gettysburg, their two main forays into Union states, put this ideology into practice: they seized scores of free black people in Maryland and Pennsylvania and sold them south into slavery. Confederates maltreated black Union troops when they captured them."