"Agriculture, United States, Labor productivity, History." . . . . "History" . "History"@en . . . . . . . . . . . . . . . . "Land and labor productivity in United States cotton production, 1800-1840" . . . "Land and labor productivity in United States cotton production, 1800-1840"@en . . . . . . . . "1800 - 1899" . . "Cotton trade, United States, History." . .