>Why did the US government do that?

Prohibition has many causes. The international treaty / 'Single Convention' was the first international treaty to prohibit cannabis.

The Single Convention on Narcotic Drugs of 1961 is an international treaty to prohibit production and supply of specific (nominally narcotic) drugs and of drugs with similar effects except under licence for specific purposes, such as medical treatment and research. As noted below, its major effects included updating the Paris Convention of 13 July 1931 to include the vast number of synthetic opioids invented in the intervening thirty years and a mechanism for more easily including new ones.

https://en.wikipedia.org/wiki/Single_Convention_on_Narcotic_...

The US uses the DEA to project political power into areas where a military presence would be rejected

My question was why did the US government do that.

If you go from the assumption that marijuana is almost as bad as cocaine and heroin — which a lot of policy makers and beurocrats pretty sincerely believed — it makes total sense.

No one actually believes that. Not anyone with any kind of power anyways.

Past and present tense usually refer to different time intervals.

That generation grew up earnestly believing that a single toke would drive you irrevocably insane, to murder, to rape, to jump from a tenth story window.

Watch "Reefer Madness" - it's reflective of the mindset these policymakers grew up with.

If you want to understand where that mindset ultimately came from, look at the history of cocaine prohibition - it boils down to racial politics.

No one smart ever believed that. Dumb people believed (and still do) that. Politicians just seized the opportunity to score some points. Same thing happens now with different topics.

Let us not judge those people as dumb please. I believed so because my parents, teachers and other government experts who visited school told me the same and I had no intention to find out myself.

It is only in modern times as I read more I learned the truth. Not everyone has time to educate themselves on these issues which many not concern them.