Antebellum architecture has to do with houses.
Antebellum, as a time period, refers to "occurring or existing before a particular war, especially the American Civil War". Antebellum architecture is referring to the style of house in that period, after the Revolutionary but before the Civil War, mostly found in the South. Those are mostly plantation style, I think. Slavery did exist during the period, especially in the South again.
(This was a 5 minute Google search cobbled together with memories of high school several decades ago, so take it with a grain of salt).