Throughout the whole history of the South, by no means the least of the evils entailed by the institution of slavery was the dread of slave insurrections which haunted every master's household; and this vague terror was at once intensified by the outbreak of civil war. It stands to the lasting credit of the negro race in the United States that the wrongs of their long bondage provoked them to no such crime, and that the Civil War appears not to have even suggested, much less started, any such organization or attempt. But the John Brown raid had indicated some possibility of the kind, and when the Union troops began their movements Generals Butler in Maryland and Patterson in Pennsylvania, moving toward Harper's Ferry, and McClellan in West Virginia, in order to reassure non-combatants, severally issued orders that all attempts at slave insurrection should be suppressed. It was a most pointed and significant warning to the leaders of the rebellion how much more vulnerable the peculiar institution was in war than in peace, and that their ill-considered scheme to protect and perpetuate slavery would prove the most potent engine for its destruction. The first effect of opening hostilities was to give adventurous or discontented slaves the chance to escape into Union camps, where, even against orders to the contrary, they found practical means of protection or concealment for the sake of the help they could render as cooks, servants, or teamsters, or for the information they could give or obtain, or the invaluable service they could render as guides. Practically, therefore, at the very beginning, the war created a bond of mutual sympathy based on mutual helpfulness, between the Southern negro and the Union volunteer; and as fast as the Union troops advanced, and secession masters fled, more or less slaves found liberation and refuge in the Union camps.