Answer:
Lincoln's decision to fight rather than to let the Southern states secede was not based on his feelings towards slavery. Rather, he felt it was his sacred duty as President of the United States to preserve the Union at all costs.
In an August 1862 letter to New York Tribune editor Horace Greeley, Lincoln confessed “my paramount object in this struggle is to save the Union, and it is not either to save or to destroy slavery.” Lincoln hoped that declaring a national policy of emancipation would stimulate a rush of the South's enslaved people into the ranks of the Union army, thus depleting the Confederacy’s labor force, on which the southern states depended to wage war against the North.
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