It's not just any union.
"America is God's crucible, the great Melting-Pot where all the races of Europe are melting and reforming!... The real American has not yet arrived. He is only in the crucible, I tell you - he will be the fusion of all races." ~Israel Zangwill
"When an American says that he loves his country, he means not only that he loves the New England hills, the prairies glistening in the sun, the wide and rising plains, the great mountains, and the sea. He means that he loves an inner air, an inner light in which freedom lives and in which a man can draw the breath of self-respect." ~Adlai Stevenson
"We dare not forget that we are the heirs of that first revolution." ~John F. Kennedy
"America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves." ~Abraham Lincoln
"My favorite thing about the United States? Lots of Americans, one America." ~Val Saintsbury
"Of all the supervised conditions for life offered man, those under U S A's constitution have proved the best. Wherefore, be sure when you start modifying, corrupting or abrogating it." ~Martin H. Fischer
"Ours is the only country deliberately founded on a good idea." ~John Gunther
"America is much more than a geographical fact. It is a political and moral fact - the first community in which men set out in principle to institutionalize freedom, responsible government, and human equality." ~Adlai Stevenson
"America did not invent human rights. In a very real sense... human rights invented America." ~Jimmy Carter
"We're Americans - with a capital A! And do you know what that means? Do you? It means that our forefathers were kicked out of every decent country in the world." ~From the movie Stripes
"The American Revolution was a beginning, not a consummation." ~Woodrow Wilson
"It predominates over the whole of society in AmericaApplication made of this principle by the Americans even before their RevolutionDevelopment given to it by that RevolutionGradual and irresistible extension of the elective qualification.
The Principle Of The Sovereignty Of The People In America" ~ Alexis de Tocqueville
Preserving the Union was much, much more than would be simply binding the territories of any other nation that existed at the time. The United States - The Great Experiment - was an evolutionary leap forward in the human race. Our Union and what it stood for became a light and an inspiration for dozens of countries and countless millions of people all across the globe.
Faced with an irresolvable problem (and oh had they tried) stemming from a mistake, a flaw, an essential contradiction that was overlooked, avoided, or irrationally justified in our newborn Union and allowed to fester until it grew into an ugly, weeping tumor, we were forced to bend our principles near the breaking point in order to save the patient. That patient was and is bigger than any one or any million of us because it stands for something irreplacable for all human beings at all times. Post surgical recovery has been slow, and the patient will never be perfect, but was it worth the operation? Damn right it was. Even if the patient hadn't pulled through it would have been worth the effort to excise that tumor.