South Carolina or Louisiana
Both answers tied to the slave trade.
When the museum opened up a few years ago, historians mentioned that Gadsen's Wharf, South Carolina was where up to 40% of enslaved Africans landed in America during the transatlantic slave trade. I think that it consistently had the highest percentage of Black people of any of states pre- Civil War.
During the domestic slave trade, New Orleans emerged as the primary destination port for the enslaved. Many of whom ended up on plantations in the state. So the state would have Africans from Senegambia+elsewhere from the French and Spanish territory eras, and AAs from the upper and lower South states.
Cultures that emerged from those port areas outward to the rest of those respective states were Black magnified.