On Lincoln

Earlier today, I was directed toward this screed against Abe Lincoln by L. Neil Smith. Now, I certainly have concerns and questions about Lincoln's commitment to the founding principles of the United States. But the proper evaluation of the man is hardly glaringly obvious. In any case, I was pleased to then read this more sober and thoughtful commentary on Lincoln from Tibor Machan.

A few questions about the Civil War plague me:

Why was Lincoln so concerned with preserving the union in the first place? (What was his philosophic justification, if any? I've never heard any explanation of this point.)

What would have happened if the North had simply allowed the South to secede? (Would this have lead to other states seceding in later years over minor issues? Even if that happened, would it have been so terrible? Would it have been worse than our present situation in which any and all secession is unthinkable?)

Why not emancipate the slaves with compensation, as happened peacefully elsewhere? (Would it have been too costly? Was the opposition to such a scheme by the abolitionists politically significant?)

If anyone has reading recommendations that might address these points (particularly the first two), I'd love to hear them.