It officially began in 1971 however it first began to take hold in 1937. In 1937 Marijuana was made illegal because people believed that the darkies would smoke their reefer cigarettes play their jazz music and rape our white women.

Harry Anslinger the commissioner of the federal bureau of narcotics (a prelude to the DEA) was quoted as saying

“There are 100,000 total marijuana smokers in the U.S., and most are Negroes, Hispanics, Filipinos and entertainers. Their Satanic music, jazz and swing result from marijuana use. This marijuana causes white women to seek sexual relations with Negroes, entertainers and any others.” “Reefer makes darkies think they’re as good as white men.”

From 1937-1971 drug laws were made to be more draconian and in 1971 the drug war was officially waged and when it was waged it was expanded and made all inclusive. We don't care what color you are anymore. If you smoke dope and you're white you're just as bad as a jazz music playing negro. And if you smoke dope and your a negro you can enjoy a federally funded ass kicking in addition to your jail time.

A former Nixon aide even admitted in recent years that the war on drugs was only started so that they could discredit the hippie movement and stop blacks and potheads from voting.

http://www.cnn.com/2016/03/23/politics/john-ehrlichman-richard-nixon-drug-war-blacks-hippie/

The war on drugs started because politicians needed a legal reason to trample on the rights of hippies and blacks. The war on drugs continues to this day because it is not in the best interest of the corporate elite that minorities and dissident whites be allowed to vote.