Why were antebellum houses built in the civil war of 1860-1865?

"Antebellum" means "before the war". Antebellum houses are those built before the Civil War. Surviving antebellum houses are rare in some places because many houses were burned during the war. There were few homes built in the south during 1861-65 because most house builders were serving in the army. After the war few people had money to build a large fine home for several generations, so, antebellum houses which survive are special.