<human>:  When did tobacco become a cash crop?
<bot>: Tobacco became a cash crop in the late 1700s, when it was cultivated in the southern United States. In the early 1800s, the first commercial tobacco factory was built in Richmond, Virginia. Tobacco became a major cash crop in the United States during the Civil War because of the high demand for it as a product of war. The invention of the cigarette in the late 19th century made tobacco a popular recreational drug, and the rise of the tobacco industry in the 20th century made it a major source of revenue for the United States.