The domestic slave trade refers to the buying and selling of enslaved people within the United States, primarily from the Upper South to the Lower South, during the 19th century. This trade was a crucial aspect of the expansion of slavery, as it helped meet the growing labor demands of Southern plantations that cultivated cash crops like cotton and tobacco. The domestic slave trade not only facilitated the economic interests of slaveholders but also contributed to the entrenchment of slavery in American society and the economy.