Not really. I was thinking more of the several unions and compacts between settlements and colonies prior to the formation of the United States. This question has the fundlemental argument of "which came first the chicken or the egg" built right in (or which is the more important the union or constitution?). Lincoln and his mentors believed wrongly that the States were formed by the power of the Government in Washington, i.e. the Union, therefore giving the Federal Government primary power over the existance of States. We all know the States were priviously colonies, totally created and formed by the efforts of the peoples who settled those territories. They, over time, for the mutual defense of each other joined into alligencies, unions or compacts. They were no centralized governments overseeing these unions; each colony was sovereign unto itself.

Jumping to the Civil War, the issue was a complex split between the North trying to preserve the Union and modify the Constitution as they saw it; the South trying to form another union and preserving (with modifications) the Constitution as they saw it. The Northern Union of States were forcing a zealous sense of law upon the Southern Union of States determined on a course of national Self-determination.

So the orignial question is too simplistic to associate to the Civil War with a simple answer because the primary issue of that war was went to the core of the rights of States. The question included the words "most important" which is very subjective and without a context to associate to whom. So the answer had to fall back unto using basic definitions to determine "importance" to preservation. I didn't give a valued weight to the importance, only the importance of the relativity to union and constitution.

David