I'm sure if you've ever hung out with a stoner then they've already probably given you the whole low down concerning the the history of marijuana in this country. Now I'm not saying that what they told you isn't true, just that maybe it was a tad bit biased towards a certain point of view. As always, the truth is a much uglier mess.
As your pothead buddy referenced, cannabis first arrived in the United States during the early colonial days as hemp and remained a major crop in many states throughout most of our country's history. However, before images of old Georgie Washington toking away fill your noggin, it should probably be said that it was just for ropes and other such fibrous products. Trying to smoke hemp to get high would be pretty much like trying to drink mouthwash to get drunk. No, the first actual cannabis product in the United States actually meant to get people high was hashish, a cannabis resin mostly used in patent medicines and by artists and other such creatives starting in the mid-nineteenth century. Hashish originally came out of the Middle East, and then spread to Europe after Napoleon invaded Egypt, where it quickly became popular amongst the intellectual elite of the time, who much like people today liked to go on and on about the possible medical applications while getting high as shit. However, hashish was expensive and hard to come by, so it really never became anything more than a rich man's drug.
Marijuana as we mostly think about it today (i.e. roasting a fatty joint) wasn't really a thing in the United States until the early twentieth century. Which is kind of strange considering it was popular throughout Latin America and the Caribbean for quite some time before. Marijuana was first brought to Brazil in the sixteenth century for use by slaves, to you know, help them be pretty chill about the fact that they were slaves and all. From Brazil it became widespread by the late 1800's as a working man's way to relax after a long day of back breaking labor for shitty pay. Around 1910, it began making its way into the United States via two main avenues. The first and largest was via a surge in Mexican immigration brought about by a civil war in Mexico that mostly just involved the various sides killing as many random people as possible. These immigrants brought their relaxant of choice with them, which rapidly began to spread amongst the existing Latin communities. The second avenue of entry was via the major port of New Orleans where it was brought in by Caribbean sailors. Marijuana became popular in jazz clubs, which subsequently became popular throughout the south, spreading it widely across portions of the black community.
It's probably at this point that your Cheech and Chong loving buddy starts going off about racism and the such leading to whitey damning the magical herb, which though likely technically true, doesn't really tell the whole story. The 1920's, for all of the glitz and glam, were not exactly the most accepting of time periods for people who looked or acted different than the majority. Anti-immigrant groups of the time most certainly found any way they could to push back against the Mexicans making their way north, including getting laws passed prohibiting the use of marijuana. However, this was largely on the local and state level. The federal government of the time mostly took the stance of as long as they got paid the vice taxes they were owed, they couldn't really give a damn what a bunch of non-white people smoked.
The main strategy used by these anti-immigration groups concerning marijuana was to claim that it caused erratic, violent, and dangerous behavior. This was of course all complete bullshit, except it kind of wasn't given that a large number of well publicized and documented cases occurred in both the U.S. and Mexico at the time, to the point that Mexico made marijuana illegal in 1920. This is where it gets complicated. You see, we don't actually know much about the marijuana of the time. Things like what were the popular varieties like, what were people lacing it with, how was it mostly consumed, and other such things have been mostly lost to history. It might be easiest to look at a report of a man smoking marijuana, going all nuts, and stabbing his buddy in the chest as made-up garbage, but reality has never been easy. Perhaps the variety smoked had a penchant for causing high anxiety in some people, maybe it was laced with heroine as was somewhat common at the time, maybe the man was drunk on rotgut liquor, maybe he was mentally unstable. The point is that things are complicated as shit. Some of the stuff we like to laugh about today as pure fiction actually happened. Was it widespread? Probably not. Was it just because of marijuana? Doubtful. Did it happen? Yes.
As has been a constant throughout American history, a few well publicized events can turn a couple of isolated incidents into a nationwide epidemic. This is exactly what happened to marijuana. The enactment of Prohibition in the 1920's led to a rapid increase in the use of pot as people looked for alternative ways to get their fix. Marijuana went from just the drug of minorities to something the white guy down the street might be experimenting with. This combined with media reports of crazed marijuana users and wildly inaccurate anti-pot propaganda (which totally didn't use sex to get people to pay attention to it) led to a rising tide of panic. In 1930 the Federal Narcotics Bureau was formed, but even then the feds refused to do much about it, seeing marijuana as being of little risk or concern compared to heroine and other hard drugs. However, that all changed in 1933 when Prohibition ended. Facing the possibility of much smaller budget and the layoff of numerous agents, the Justice Department switched its stance on marijuana from "no worries man" to "that shit is going to make everyone violent hedonists if we don't do something about it". In 1937 marijuana was made illegal in the U.S. You know the rest of the story.