Two words "military necessity" are made to cover nearly the entire argument for emancipation in September, 1862, but in just what manner the military prowess of the North was to be increased was not at first indicated.

In 1864, Lincoln declared that after the failure of successive efforts to persuade the border states to accept compensated emancipation he had believed there had arrived the "indispensable necessity for military emancipation and arming the blacks[874]." Repeatedly in later defence of the proclamation he urged the benefits that had come from his act and asserted that commanders in the field "believe the emancipation policy and the use of coloured troops constitute the heaviest blow yet dealt to the rebellion[875]." He added: "negroes, like other people, act upon motives.

Why should they do anything for us, if we will do nothing for them?
If they stake their lives for us, they must be prompted by the strongest motive, even the promise of freedom." There is no note here of stirring a servile insurrection; nor did Lincoln ever acknowledge that such a purpose had been in his mind, though the thought of such possible result must have been present--was, indeed, present to most minds even without a proclamation of emancipation.

Lincoln's alleged purpose was simply to draw away slaves, wherever possible, from their rebellious masters, thus reducing the economic powers of resistance of the South, and then to make these ex-slaves directly useful in winning the war.

But after the war, even here and there during it, a theory was advanced that an impelling motive with the President had been the hope of influencing favourably foreign governments and peoples by stamping the Northern cause with a high moral purpose.