It actually was a consipiracy, of sorts. I did a sociogical paper in college on marijuana and looked at the history of the drug in the US. The cannabis plant can be smoked in two different forms: hashish and what we refer to as marijuana. Hashish has a very bad reputation - hash dens, the word assassin comes from a reference to Hashsashins (killers for hire who would smoke hashish before doing their killing).

In America, marijuana was steadily used by physicians for several medical problems. It was included in many early medical texts.

During the twenties and prohibition, marijuana had started to become very popular among the black jazz community and then into the black urban communities of the North. Once prohibition was withdrawn, a number of 'stories' started to float around about this "killer" drug. That it caused people who smoked it to go crazy and kill people. They also made marijuana out to be a poor, black-person drug.

About the same time a large push to cut down on the hashish trade in other parts of the world. Since these are two drugs from the same plant their effects or inaffects would become mingeled. One source, I remember, stated that these rumors were actually started by those in the struggling beer and liquor industry, along with a contingent from the tobacco industry. Those two industries feared that people who smoked marijuana would use their products less.

In 1937 the Marijuana tax act was passed, and then during the '60s-70s the drug was moved to schedule 1. There have been several attempts by the medical community and even some legislatures to relook at marijuana as medically useful drug - but the Reagan years has killed any of those actions up till now.

Personally, I think that until we can control the alcohol & tobacco industries in their kickbacks marijuana is going to have a rough road to legality here in the states.