Use the adjective antebellum to describe something that happened before the American Civil War. You could talk about touring a historic antebellum plantation house in Georgia, for example.
When historians describe the time before the Civil War, they call it "the antebellum period." The southern United States at that time is often called "the antebellum South." You might describe a plantation, an antique dress, or other artifacts of that historical period as antebellum. Officially, the word antebellum can describe the time just before any war, but it's usually used in reference to the Civil War. It comes from the Latin phrase ante bellum, literally "before the war."
