"Marijuana essentially became illegal in 1937 pursuant to the Marijuana Tax Act.39 The use of marijuana required the payment of a tax for usage; failure to pay the tax resulted in a large fine or stiff prison time for tax evasion.40 Drug prohibition was elevated to another level by targeting 'marijuana,' a plant that had never demonstrated any harm to anyone.41
"Anslinger’s [Harry J. Anslinger, the first Commissioner of the Federal Bureau of Narcotics] efforts to eradicate marijuana continued when Anslinger sought similar anti-narcotic laws against marijuana at the state level.42 Guided by Anslinger’s policy direction, states began passing their own laws or adopting more strident versions of federal laws.43 By 1952, nearly all states had anti-narcotic laws in place.44"
Brian Gilmore, Again and Again we Suffer: The Poor and the Endurance of the "War on Drugs", 15 U.D.C. L. Rev. 59 (2011).