J. S. Johnston to Thomas Butler, March 12, 1832.
[renewed concern emereged in Louisiana about the rapid growth of the state's slave population and the outward flow of capital to slave-selling regions. ]
J.S. Johnston thought the new restrictions  might prevent the state from being "drained of our capital for the purchase of more Negroes." He reasoned that the cessation of the interstate slave trade might prompt Virginians and other upper South slaveholders to move to Louisiana rather than simply selling off slaves to Louisiana buyers..Virginia would "feel the difference between selling slaves for money and having them carried away by her own people," a prospect that he predicted "will be as beneficial to us as it will be injurious to her."
Mississippi, 1828, Governor Gerand Brandon recommended closing the internal slave trade [again] because he believed that Mississippi had become a "receptacle for the surplus black population of the Middle States."
"The assertion that slavery wouldn't have worked in such agricultural regions as California and Oregon I find extremely puzzling."
In order for a Southern style plantation system to work, you must be able to independently sustain large bodies of human life for free and produce a large money making crop quickly. This could not be done in California or Oregon prior to the introduction of a reliable railroad system connecting the West to the East and, most importantly, access to abundant water. These states are mostly at high elevations exceding the frost line, have short rain seasons in large portions of their areas, are extremely hot or cold, covered in large tracts of unusable, arid lands. And soils that will only produce crops if irrigated. Until the aquaducts and dams, California was then and still can be- a big, dusty desert.
"By increasing the population of non-voting-but-still-counted slaves into other territories, they increased their political power. Which they needed to do, because the Northern states were having a large influx of immigrants, mostly Irish. "
So by seceding, they would protect this "advantage"? Within the Confederacy they no longer had the protection to the system that the Union provided and each seceding slave state nullified their political power; since now they were all slave states represented within their own Congress. By seceding, they destroyed their market expansion for slaves and the ability to prevent their running away through a large porous border, to a foreign land, that would not have a legal reason to return their property? Either they were extremely stupid [they weren't] or they really didn't care about the institution of slavery enough to worry about the consequences of secession.