White supremacy was, in effect, what the War was about.
[...]
White supremacy over who?
Are you suggesting the Confederates went to war to assert their "supremacy" over the Black African slave class? That audacious notion carelessly confuses the social status of the negro in America in 1861 with that of today.
While it is true that slavery played a major role in fomenting the Civil War the provocative issue was not
morality but
economics. The North was opposed to slavery because of the threat it posed to the salaried White working class which had become the engine of the rapidly developing Northern economy: well-paid workers had money to spend, thereby promoting the growth of business and industrial progress. The introduction of slaves into that equation would promptly collapse it.
That economics was the end game is irrelevant here. Slavery was already a moral dilemma, had been for centuries, and the US was already lagging behind its contemporaries in the world, the then-colonial powers all having abandoned it by then. The Republican Party itself, as well as earlier parties such as the Free Soilers, had been formed to address it. Bottom line being,
without white supremacy, that system of slavery --- whatever its economic implications might be --- could not exist.
Or to put it a slightly different way, without the racism that maintains that one race should dominate another, race-based slavery --- an entirely new concept developed by the Atlantic slave trade -- has no basis for its own existence.
Therefore, regardless what the ultimate impact on the economy of one region/country or another might be, you cannot have that model of slavery without white supremacy, and you cannot have white supremacy without racism. Therefore white supremacy
must be maintained in order for the African slavery to be maintained.
This is not to suggest the Union's cause was entirely noble/altruistic and the Confederacy's was entirely ignoble, or that economics played no part. Of course it did. It's more a contrast of the latter's resistance to progress, to accept the moral basis to which the world was already turning, and to which most of it had turned --- a basis that in practical terms made the slavery system impossible.
I tried to note all this originally with the phrase "in effect".