There has been some debate about the true origin of the sectional sofa, many believe it's origins are in the
early 1800s, prior to the Civil War in America when hired craftsmen created a custom sofa comprised of three sections that latched together in Fredericksburg, Virginia. Most of the original pieces were destroyed during the war, but as the Victorian era approached, the sectional came back as a popular piece for those who liked to entertain in their homes.
The original sectionals consisted of two couches connected, tufted, laminated, and less commonly featured corner pieces. During the mid-century modern era, the sectional sofa was considered the sleek, industrial profile of contemporary furniture and quickly rose to popularity thanks, in large part, to department store catalogs.
These early concepts introduced the theory of customization that we know today, where a sofa can be broken down into modular pieces with seats and seat cushions and can be tailored to the size of the room. They are also much easier to mass-produce and ship.