Before the opening of actual military operations, while there was still hope of some peaceful solution, British opinion had been with the North on the alleged ground of sympathy with a free as against a slave-owning society. But war once begun the disturbance to British trade interests and Lincoln's repeated declarations that the North had no intention of destroying slavery combined to offer an excuse and a reason for an almost complete shift of British opinion. The abolitionists of the North and the extreme anti-slavery friends in England, relatively few in number in both countries, still sounded the note of "slavery the cause of the war," but got little hearing. Nevertheless it was seen by thoughtful minds that slavery was certain to have a distinct bearing on the position of Great Britain when the war was concluded. In May, 1861, Palmerston declared that it would be a happy day when "we could succeed in putting an end to this unnatural war between the two sections of our North American cousins," but added that the difficulty for England was that "We could not well mix ourselves up with the acknowledgment of slavery[855]...."

Great Britain's long-asserted abhorrence of slavery caused, indeed, a perplexity in governmental attitude. But this looked to the final outcome of an independent South - an outcome long taken for granted. Debate on the existing moralities of the war very soon largely disappeared from British discussion and in its place there cropped out, here and there, expressions indicative of anxiety as to whether the war could long continue without a "servile insurrection," with all its attendant horrors.

On July 6, 1861, the Economist, reviewing the progress of the war preparations to date, asserted that it was universally agreed no restoration of the Union was possible and answered British fears by declaring it was impossible to believe that even the American madness could contemplate a servile insurrection. The friendly Spectator also discussed the matter and repeatedly. It was a mistaken idea, said this journal, that there could be no enfranchisement without a slave rising, but should this occur, "the right of the slave to regain his freedom, even if the effort involve slaughter, is as clear as any other application of the right of self-defence[856]." Yet English abolitionists should not urge the slave to act for himself, since "as war goes on and all compromise fails the American mind will harden under the white heat and determine that the cause of all conflict must cease." That slavery, in spite of any declaration by Lincoln or Northern denial of a purpose to attack it - denials which disgusted Harriet Martineau - was in real fact the basic cause of the war, seemed to her as clear as anything in reason[857]. She had no patience with English anti-slavery people who believed Northern protestations, and she did not express concern over the horrors of a possible servile insurrection. Nevertheless this spectre was constantly appearing. Again the Spectator sought to allay such fears; but yet again also proclaimed that even such a contingency was less fearful than the consolidation of the slave-power in the South[858].

Thus a servile insurrection was early and frequently an argument which pro-Northern friends were compelled to meet. In truth the bulk of the British press was constant in holding up this bogie to its readers, even going to the point of weakening its argument of the impossibility of a Northern conquest of the South by appealing to history to show that England in her two wars with America had had a comparatively easy time in the South, thus postulating the real danger of some "negro Garibaldi calling his countrymen to arms[859]." Nor was this fear merely a pretended one. It affected all classes and partisans of both sides. Even official England shared in it; January 20, 1862, Lyons wrote, "The question is rapidly tending towards the issue either of peace and a recognition of the separation, or a Proclamation of Emancipation and the raising of a servile insurrection[860]." At nearly the same time Russell, returning to Gladstone a letter from Sumner to Cobden, expressed his sorrow "that the President intends a war of emancipation, meaning thereby, I fear, a war of greater desolation than has been since the revival of letters[861]." John Stuart Mill, with that clear logic which appealed to the more intelligent reader, in an able examination of the underlying causes and probable results of the American conflict, excused the Northern leaders for early denial of a purpose to attack slavery, but expressed complete confidence that even these leaders by now understood the "almost certain results of success in the present conflict" (the extinction of slavery) and prophesied that "if the writers who so severely criticize the present moderation of the Free-soilers are desirous to see the war become an abolition war, it is probable that if the war lasts long enough they will be gratified[862]." John Bright, reaching a wider public, in speech after speech, expressed faith that the people of the North were "marching on, as I believe, to its [slavery's] entire abolition[863]."