The Deep South is a descriptive category of the cultural and geographic subregions in the Southern United States. Historically, it is differentiated from the "Upper South" as being the states most dependent on plantation-type agriculture and slavery during the pre–Civil War period. The Deep South was also commonly referred to as the Lower South or the Cotton States. Before the out-migrations at the first half of the 20th century, African-descended peoples comprised the majority of the population in numerous areas and some states. Today, the Deep South is usually delineated as being those states and areas where cultural elements most often thought of as "Southern" exist in their most concentrated form.