Bottom line is that the South was fighting to preserve an antiquated system that was dependent upon agriculture. The war was a conflict between two cultures, but it was NOT between two seperate nations except in the minds of those diehards who still don't believe in a UNITED States of America. A divided country would have been taken advantage of by the European powers as they sought to keep America off of the world stage and pitted one side against the other.
The collapse of the American republic into two or more federations would probably have led to large scale empire building not only in the United States, but in Latin America. Remember that Napoleon III of France conquered Mexico in defiance of the Monroe Doctrine at a time when the Washington government had its hands full with the Southern secession. France, England, and other European nations would have recolonized the entire hemisphere. Neo-Confederates overlook the fact that the European states that were carving up Asia and Africa into colonies inn the late 19th Century would have done the same in Latin America and even the American West. If the Confederacy aligned with England and the remnants of the USA with Germany, World War I battles might have been fought near the Ohio and Missouri Rivers, as well as near the Seine and Rhine.
The war was a conflict between two cultures, but it was NOT between two separate nations...
The primary characteristic that defines America as a nation is a common idea and vision, not ties of race and ethnicity. Ethnically speaking, the South of 1860 was basically unchanged from the Southern colonies of 1776: a British Protestant majority and a mostly enslaved African minority. The North, originally predominantly British and Protestant, had experienced large immigration waves from Ireland, Germany, Scandinavia, and the Low Countries. While these immigrants were more or less physically indistinguishable from the descendants of British colonial settlers, there were considerable language and religious differences. Nonetheless, the beginning of the "Melting Pot" was in evidence. Several Union generals were first or second generation Irish or German Americans (Sheridan and Schurz, for example).
Had the Southerners achieved independence, there would have been two nations as distinct as the United States and Canada, or Sweden and Norway.