How long would slavery had lasted if the South decided NOT to secede?

[1-Old-Man]

29. The spread of slavery into the new territories was led more by rice and cotton than corn.

It is also very important to understand the differences in the slave trade between the old southeastern money and the newly developing agricultural lands in the west. Virginia and to a lessor extent Maryland had become slave breeding centers instead of slave labor users. Also keep in mind the types of crops where slave labor is useful, those which require full season attention. Tobacco, cotton, rice, as opposed to the field crops where large animals are (were) used for large area tillage and to the extent harvest is mechanized there too, but the rest of the time your slaves have as little to do as a John Deere harvester in December except the slaves still have to be fed (as do horses and oxen). So as slavery moved to the new territories and they grew to large enough populations to support a bid for Statehood the political maneuvering brought slavery with it as sure as clouds bring rain there wasn't much chance of that slavery being sustainable long term. As I said above, sooner or later we were going to bump up against Canada or the Pacific Ocean, and there it would end.