This well researched piece comes from a colleague's blog and is worth the read...
"Many people today think maintaining the integrity of the union is constitutional; never stopping to think their position is neither congruent nor synonymous. The irony is that in the way Lincoln preserved the union he destroyed the voluntary association and State autonomy aspects of the Constitution and made the central government supreme in the United States, which it was not up until that time."
Read the whole thing at American Founding Principals
While you are there, cruise his other articles....lots of good stuff.