Alternative History and the survival of slavery into the 20th century

There have been various alternative histories which imagine what the present would be like if the Confederacy had won. With a Confederate victory these fictions focus on the persistence of slavery into the present day.

To have a Confederate victory they pose that a Confederate military victory at some battle, or the entry of a European power makes a Confederate victory possible.

The persistence of slavery into the 20th or 21st century is always imagined as being possible through Confederate victory.

However, there is one way slavery could have persisted into the 20th century. It very likely would have made it into the 20th century easily IF THERE HAD BEEN NO CIVIL WAR.

The Civil War started because a lot of slave owners in the slave states panicked and reacted and choose the path of secession.  There is really nothing like war to bring down a slave society.

In general slaves will support the enemy belligerent of a slave society and often enlist in their armies and help in many other ways. In the Civil War many African Americans enlisted in the American Army.  Also, during a war you have an enemy at the front and essentially an enemy at home waiting for the right opportunity to flee or take revenge or both.

There was no possibility of a constitutional amendment being passed to abolish slavery as long as the slave states didn't secede. Yes, there could have been legislative actions making slavery more difficult to sustain. Over time as new states were admitted and as some states became free states, there might have been the opportunity for a constitutional amendment but that would have been fairly far in the future. For a 3/4th majority there would have had to have been 44 to 48 states depending on how many slave states remained and every, each and every, none-slave state would have had to been supporting the effort.

Even then emancipation could have been very gradual and would very likely been on the terms dictated by the slave states.

In alternative history it needs to be imagined that slavery would have happened with no Civil War and not with a Confederate victory. I think why this isn't imagined is because the American historical imagination is in the thralls of the ideas of American exceptionalism.