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In 1831 Virginia nearly abolished slavery. The gist was that the state would have gradual manumission with the peculiar institution more or less phased out by the 1860s. Though this was an antislavery measure it was more anti-black than anti-slave - Freedmen were to be banned from the state and the intention was that all slaves would either be sold further south or deported to Liberia (with the state requiring many newly freed slaves to have to work to make enough money to pay for their passage to Liberia). White Virginians wanted a white Virginia. There was also a big push for this from West Virginians who didn't like the political power of the planters.

One ramification might be that in the short term slaveocrats might be *more* expansionist. With one fewer slave state in the Senate, there'd be a strong inclination to make up for Virginia's shifting into the free state column. This might be as simple as Florida or Texas being admitted as multiple states or the US being more aggressive with matters like Cuba or William Walker's Nicaragua. Virginia meanwhile probably sides with the expansionists despite being a free state because Virginians will want to send their slaves somewhere.

Additionally, we may see slavery being further cemented in other states. Odds are a lot of Virginian slaveholders will move to other states, further influencing politics there. Maybe Virginia's example might inspire other states (KY, MD, and NC in particular) to follow suit, but I think that it's more likely that we'll just see more movement of slaves and slaveholders into other states. Maryland and Delaware might be another matter however.

Virginia likely is much more industrialized here and probably attracts more immigrants, changing the state's character. Odds are there will still be fields that need to be worked and it'll be immigrants working them if blacks are banned from the state.
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