What were the reasons Lincoln ultimately issued the emancipation

The proclamation was a presidential order and not a law passed by Congress, so Lincoln then pushed for an antislavery amendment to the U.S. Constitution to ensure its permanence. ... Lincoln's handwritten draft of the final Emancipation Proclamation was destroyed in the Chicago Fire of 1871.

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to force terrorists groups to stop attacking western targets using massive military force.

it was bribing i think i might be wrong though