Thank you all very much. Very helpful.
davidmich
It has already been pointed out that Lincoln limited the scope of the Emancipation Proclamation in order to avoid exceeding his constitutional authority. There were political reasons, as well. He’d have lost a lot of support in the non-rebel slave states if he had tried to free the slaves there. This was something he couldn’t afford in the middle of the war. The existing proclamation, as weak as it was, upset some on the union side. It helped set off the New York draft riots, for example.
Lincoln was walking a tightrope in dealing with this issue. One of his goals was to undermine those Europeans who wanted to help the Confederacy. He did this by making the war at least partly about abolition. He couldn’t go too far in this direction without alienating those at home who thought the was should have been about saving the union, not eliminating slavery.