Lincoln issued the final Emancipation Proclamation on the first of the new year as promised in his Preliminary Proclamation of September 22, 1862. Keenly aware of the constitutional limits of his office, the president justified the new policy on the basis of military necessity and the war powers invested in the presidency. With the precision of a constitutional legal brief, Lincoln's document carefully crafted its impact upon slavery in those areas that had seceded and excluded states that had remained in the Union but still maintained slavery. Lincoln remained true to his famed response to Horace Greeley that he would abolish slavery only as a necessary means to restore the Union. With battle casualties rising and the prospects of victory diminishing, he believed the time had finally arrived to attack the central cause of the war. In a dramatic change from the Preliminary Proclamation, Lincoln authorized the recruitment of African Americans for the army. By the late summer of 1862, he had been persuaded by the writings of George Livermore, a Boston merchant, that the Founding Fathers had supported use of black troops in the American Revolution and that they had performed with distinction. Nevertheless, to Lincoln and the War Department black recruitment remained a volatile experiment. In response to the Emancipation Proclamation, rallies from Boston to San Francisco celebrated the move, heralding the beginning of the end of slavery. While all thanked Lincoln for keeping his word, most Northern blacks gave credit to God for the dramatic change in war policy, rather than to the president, who had heretofore professed a greater interest in colonization than in freedom.