If secession of the deep south was allowed, likely slavery would be gone within a few decades and readmission into the Union possibly delayed until world war 1, simply because of the issue of tarriffs. I think tensions Mexico and Cuba, and an ATL Zimmerman telegram might offer the cassus belli that economic concerns and the non existence of slavery that de facto would be the reasons for rejoining.
the United States and the south would be both more economically advanced today by a little. Race relations might not be markedly different. Proof of this can be seen in nearly every nation on Earth that had ended slavery without either war or general insurrection tends to have decent race relations, though not perfect race relations. We might se de facto, instead of de jure segregation, which still exists today (face it, how many people even in the 1990s lived in diverse neighborhoods?)
the civil war captivates the public imagination as it feels like our nation had to atone for the sin of slavery with the death of so many, because as the Bible says without the shedding of blood there is no forgiveness of sins. However, pretty much every nation on Earth with slavery ended it cheaper, with no loss of life, and no national destruction. Of course people would not know it at the time but everyone of every race was probably better without the civil war in the long run (in the short run, blacks are obviously better off emancipated.)
the knock on effects on us policy are profound. If secession is allowed, it becomes a viable policy. We would hear threats of it over the decades but ironically I think that the rise of modern identity politics might lead to real secession (an OTL Obama or Trump might lead to a state or two actually seceding, but they will come crawling back when the lack of federal funds take their effect.)
all in all, America would be very similar economically and even socially, but our political maneuvering will be literally and rhetorically different.
the United States and the south would be both more economically advanced today by a little. Race relations might not be markedly different. Proof of this can be seen in nearly every nation on Earth that had ended slavery without either war or general insurrection tends to have decent race relations, though not perfect race relations. We might se de facto, instead of de jure segregation, which still exists today (face it, how many people even in the 1990s lived in diverse neighborhoods?)
the civil war captivates the public imagination as it feels like our nation had to atone for the sin of slavery with the death of so many, because as the Bible says without the shedding of blood there is no forgiveness of sins. However, pretty much every nation on Earth with slavery ended it cheaper, with no loss of life, and no national destruction. Of course people would not know it at the time but everyone of every race was probably better without the civil war in the long run (in the short run, blacks are obviously better off emancipated.)
the knock on effects on us policy are profound. If secession is allowed, it becomes a viable policy. We would hear threats of it over the decades but ironically I think that the rise of modern identity politics might lead to real secession (an OTL Obama or Trump might lead to a state or two actually seceding, but they will come crawling back when the lack of federal funds take their effect.)
all in all, America would be very similar economically and even socially, but our political maneuvering will be literally and rhetorically different.