"Physically speaking, we cannot separate. We can not remove our respective sections from each other, nor build an impassable wall between them. A husband and wife may be divorced, and go out of the presence, and beyond the reach of each other; but the different parts of our country cannot do this. They cannot but remain face to face; and intercourse, either amicable or hostile, must continue between them. Is it possible, then, to make that intercourse more advantageous or more satisfactory, after separation than before? Can aliens make treaties easier than friends can make laws?"
Abraham Lincoln, First Inaugural Address
Cant separate, huh?
We could have had peaceful separation and free trade, but they wanted the tariff collections at the southern ports, which constituted 70% of the revenue which fed the federal government.