First, a bit about my American Background:
My mother's side are Liberal intellectuals from Wisconsin, Clevelend, and New York. (Sociologists, NIH Scientist, activists, population council et cetra)
Father: South Carolina Democrats turned Conservative Republicans (one of my cousins is a Conservative Republican state senator, many religious fundamentalists (and I do mean Fundamentalists), war vetrans in almost every American conflict)
My Maternal Grandmother, and Paternal Grandfather moved to Maryland, the compromise state, (that's not the real motto but it should be) My Mother and Father married. So, seeing things from both extremities might be useful.
Civil War History is not an area of expertise of mine, one of my brothers is a Civil War buff though. I am more of a World History/Politics/Relations buff (not as sexy to many Americans, but its important).
First off, people mentioned some reasons for the South losing... well you forgot to mention a very important one: Railroads. The northa had a lot more rail road capacity and tracks than the south. This, needless to say, was very important.
Second, suppose we throw out the legality argument for the Civil War, suppose all laws are not a measure of Justice. Suppose there were unscrupulous reasons for the Unionists et cetra...
I'm sure, water, that you are happy America exists as a free and independent entity aren't you? France had unscrupulous reasons for helping America, surely America would not be where it is today without that help.... leaving legality out, it was good thing for America that France did help. (I've heard people say: well, only Francophiles make the argument that France had a huge impact on America's success in the Rev. War, it is Historical agreement that they did. The statistics and regional pressures speak for themselves)
So, you are going to tell me honestly, water, that you think America would be better off had the South broke off from the union? After the civil war, America flooded world markets with its goods, steel was very important, far surpassing any European power... so was cotton at one point... but if America was fractured in this way, are you going tell me we would be the better for it? (what about slavery, or the residual racism, the system needed cleaning)
Now, RKL, don't try and justify the Civil War on legal grounds, that's so Lawyerly New Yorkish of you

The moral argument stands by itself. What is the point of dragging Supreme Court verdicts into this means nothing... The victors write the History and the laws in most wars, it doesn't hold any moral weight by itself. Ex post facto legalizing of presidentail decisions are just a nod of approval: it still comes back to a moral argument, just an official acknowledgement...