The threat of emancipation was a war measure used by Lincoln against the States that were wanting to secede. He offered to let them keep their slaves if they agreed to stay in the Union, because slavery was more economically important in the South than in the North (yes the North had Slavery too). The original dispute was over the so called ‘tariff of abominations’. Lincoln didn’t think the negroes could be integrated into society and proposed sending them back to Africa. Lincoln gets credit for emancipating the slaves, but he didn’t do it out of humanitarian considerations.