What if the Missouri Compromise and the Compromise of 1850 didn't go the way of the South, and Dred Scott v Sanford went the other way (I know Justice Taney and most of his fellow Justices were slave-owning southerners, but just stick with me here), would the South have seceded 40 years earlier? They would be in the best position possible, most of their land hasn't been converted to solely cotton farming, the British can be realistic allies as the Oregon territory is still contested between them and the US, and the Brits haven't made Slavery illegal yet. The north isn't nearly as industrialized as it would be by 1860. I'm thinking we get rid of Henry Clay and have the North stop catering towards the sound, like Filmore not signing the Fugitive Slave act in 1850.
What I am looking for is one PoD to start off the chain reaction that would lead to either all or most of these things happening; the main goal here is Southern Succession with all Slave states (Virginia, Kentucky, The Carolinas, Missouri, Georgia, Alabama, Florida, Tennessee, Mississippi, Louisiana, etc) not before 1820 and not after 1860. The earlier the better. Remember, the south doesn't have to win, I don't care about that, I don't even care about the Civil War aspect.