I'm not disagreeing with you but it was a complicated issue. The Union was split over the issue of slavery for most of the war. Union states like Missouri, Kentucky, Maryland and Delaware held well over 400,000 slaves and to immediately declare it illegal would have put those states closer to joining the Confederacy (maybe not Delaware). This is forgotten in today's history. Add the number of occupied territory at the signing of the E.P. and you got half the slave population being regulated by the Union.
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David Upton