What the South had for much of the 20th century was much closer to apartheid. Blacks were not allowed to vote, for example, or to exercise generally protected rights that whites had, such as the right to assemble and petition the government for redress of grievances. In a merely segregated situation, different races would be prevented from mixing but treated by the government as equal citizens. That did not come close to happening: the various Southern governments did not even make a pretense of being neutral arbiters of segregation, but were quite openly White governments, acting as shamelessly violent partisans of the White population's interests.
Louisville, Kentucky, had segregation but not Jim Crow. The black population was a minor but important voting bloc, that could unite to oust mayors who really crossed a line with the racist bullshit. But make no mistake about how people were "treated as equal citizens" under segregation. When the city started establishing a system of large parks, black people were to be excluded, and when the black community protested, the city created a smaller, special park that black people could visit. Add to that the problems of educational segregation, political corruption, voter fraud and intimidation.
The North was not much better, where racial segregation in places like Chicago and Seattle was enforced through redlining, blockbusting, restrictive deed covenants, &c., and outright government policy.
Much of the country was ruled by an explicit white supremacist ideology for much of the 20th century, often enforced through open terroristic violence (lynching).
