However, when public disquiet at the crime and social damage caused by alcohol prohibition led to its repeal, Anslinger saw his position as being in danger.
To enable him to keep his army of drug enforcers, he created a new drug threat: cannabis, which he called marijuana to make it sound more Mexican. Working with a newspaper magnate, William Randolph Hearst, he created hysteria around the impact of cannabis on American youth and proclaimed an invasion of marijuana-smoking Mexican men assaulting white women. The ensuing public anxiety led to the drug being banned. The US then imposed its anti-cannabis stance on other western countries and this was finally imposed on the rest of the world through the first UN convention on narcotic drugs in 1961.
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So the short answer to the question “why are (some) drugs illegal?” is simple. It’s because the editors of powerful newspapers want it that way. They see getting drugs banned as a tangible measure of success, a badge of honour. And behind them the alcohol industry continues secretly to express its opposition to anything that might challenge its monopoly of recreational drug sales. But that’s another story.
https://www.theguardian.com/commentisfree/2015/oct/28/why-are-drugs-illegal-google-answer