Hemp in US History
"During World War I, some hemp cultivation occurred in several states, including Kentucky, Wisconsin, California, North Dakota, South Dakota, Minnesota, Indiana, Illinois, Ohio, Michigan, Kansas, and Iowa (Ehrensing 1998). The second world war led to a brief revival of hemp cultivation in the Midwest, as well as in Canada, because the war cut off supplies of fiber (substantial renewed cultivation also occurred in Germany for the same reason). Until the beginning of the 19th century, hemp was the leading cordage fiber. Until the middle of the 19th century, hemp rivaled flax as the chief textile fiber of vegetable origin, and indeed was described as 'the king of fiber-bearing plants,—the standard by which all other fibers are measured' (Boyce 1900). Nevertheless, the Marihuana Tax Act applied in 1938 essentially ended hemp production in the United States, although a small hemp fiber industry continued in Wisconsin until 1958. Similarly in 1938 the cultivation of Cannabis became illegal in Canada under the Opium and Narcotics Act."
Small, Ernest and Marcus, David , "Hemp: A New Crop with New Uses for North America," Trends in New Crops and New Uses (West Lafayette, IN: Purdue University Center for New Crops and Plant Products, 2002), p. 284.