A war of numbers. The North was both more popilated and industrialized, and therefore had control of most of the weapons and ordinance production. The South being less populated and industrialized was thought to be easier to gain control of, and there had been
a gold rush not long before the Civil War, which would interest powerful people in North to regain control of a seceded part of the union. Since the North wrote the history books, their version of history was always going to be the more popular and noble sounding version of history, but not everything in a book is to be taken without
a grain of salt, any more than any other source. Most wars are money/resource/power struggles once you get below the surface, with headlines about abolition and emancipation from slavery being
icing on the cake that gives people a warm, boosted ego, even if the people that started the war had no true interest in or gave a fuck about a single black/ African descendant since it's rare that ones that started the war are the same ones fighting in it (Washington being an exception).