One of the most startling developments in recent US politics is how quickly support for marijuana legalization grew in just a few years. Ten years ago, 36 percent of Americans supported legalizing pot. Today that number is at 58 percent, according to Gallup.

The result: Since the beginning of 2012, we've gone from no states legally allowing the recreational use of marijuana to four states and Washington, DC, doing so, thanks to voter-supported ballot initiatives. And 2016 could open the floodgates: At least five more states, including California, will likely have marijuana legalization initiatives on their ballots, potentially making it so tens of millions of Americans will live in a state where pot is legal.

How did the marijuana legalization movement take off so quickly?

There are many factors, but one of them is undoubtedly the internet.

For the past century, most of the information Americans received about drugs came from the government, anti-drug groups, and media — but these reports were often very sensationalist, based on the claims of law enforcement and government officials who have a vested interest in continuing the war on drugs. The internet helped break this monopoly on information about drugs, including pot — not only helping Americans develop more nuanced perspectives about drugs and their effects, but also opening people to the idea that maybe some of these drugs aren't so bad, so they should be legally allowed.

"For decades, most Americans were only able to get information about the effects of marijuana itself, and the policies prohibiting it, from the government or from mainstream media outlets who tended to source their stories mostly from the government," said Tom Angell, head of the pro-legalization Marijuana Majority. "But as more Americans got online, they could access alternative perspectives from a growing number of websites and organizations dedicated to providing a more realistic picture."

Anti-drug rhetoric has been out of control for more than a century

Reefer madness: It's now a phrase that's widely mocked in discussions about marijuana — something so absurd that just saying it can elicit laughs.

But back when the term was first used, it was not a joke. It was a serious phrase used to describe what anti-drug groups — and the federal government — saw as a threat: that marijuana would cause people to act wildly, and even commit violent and sexual crimes.

To be clear, marijuana has not been linked in any way to violence. (That honor belongs to alcohol.) Nonetheless, in the 1930s, during the early days of marijuana's mainstream entry to the US, this exotic plant was feared, as demonstrated by the 1938 movie Tell Your Children, also known as Reefer Madness.

This was not the first or last time that America would use sensationalism in its war on drugs. Instead, unhinged anti-drug rhetoric has been standard for more than a century — going back to the country's first major anti-drug laws, the Harrison Narcotics Tax Act of 1914 and the Marijuana Tax Act of 1937.

Harry Anslinger, the first head of the Federal Bureau of Narcotics, predecessor to the Drug Enforcement Administration, built support for anti-marijuana laws in the 1930s in part by blaming a Florida ax murder on the drug:

An entire family was murdered by a youthful addict in Florida. When officers arrived at the home, they found the youth staggering about in a human slaughterhouse. With an axe he had killed his father, mother, two brothers, and a sister. He seemed to be in a daze… He had no recollection of having committed the multiple crimes. The officers knew him ordinarily as a sane, rather quiet young man; now he was pitifully crazed. They sought the reason. The boy said that he had been in the habit of smoking something which youthful friends called 'muggles,' a childish name for marijuana.

Since the federal government launched its modern war on drugs in 1971, this kind of rhetoric has been a recurring theme in the government's anti-drug efforts. The 1980s, boosted by Nancy Reagan's "Just Say No" campaign, were filled with hyperbolic anti-drug ads — including an infamous ad that suggested a person's brain would be scrambled after any drug use, and one that compared drug abuse to literal slavery.

In the past few decades, much of this rhetoric culminated in anti-drug campaigns for schoolchildren. The anti-drug program DARE, for instance, claimed in now-deleted "fact sheets" that marijuana has no medical value, weakens the immune system, and causes insanity and lung disease — claims that are false or, at the very least, widely disputed by the research on pot.

Sometimes the anti-drug messaging even took a racist turn. In 1914, the New York Times ran an article that claimed "Negro cocaine 'fiends' are a new southern menace," suggesting that cocaine made black people violent and impervious to bullets. Drug expert Carl Hart explained in a piece for the Nation that this type of racist rhetoric was actually standard in the drug war: Time and time again, the effects of drug use were exaggerated to suggest these substances would turn black, Hispanic, and Asian men into dangerous maniacs, typically in order to attack a helpless woman.

Take, for instance, these alleged quotes from Anslinger, reported by journalist Maia Szalavitz:

"Reefer makes darkies think they're as good as white men." … "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."

What makes this anti-drug rhetoric so bad, beyond its factual inaccuracy and general ugliness, is that it doesn't even work to reduce drug use. Various studies show DARE, for example, failed to significantly cut drug use among participants. Why? For one, teens were simply too good at catching and dismissing clear exaggerations about the detrimental health effects of relatively harmless drugs like marijuana, and that helped discredit DARE's overall efforts.

"Especially with teens, you've got to be credible," Michael Slater, an expert at Ohio State University who's studied anti-drug campaigns, previously told me. "They've got great BS thermometers."

So these messages don't just actively misinform the public; they also don't appear to actually accomplish what they seek to do — reduce drug use. Still, as Americans' sole source of information about drugs for much of the past century, they helped suppress support for laxer drug policies for decades.

The internet helped mellow out talk about drugs

Then the internet came — and its free flow of information exposed millions of Americans to a different narrative about drugs, one that's more nuanced than the exclusively negative messages from before.

Marijuana legalization advocates are well aware of this. In the conversations I've had on legalization's quick rise in support, multiple pot activists have credited the internet with helping normalize and build support for their movement. (The research supports this concept: One review of the literature concluded that the internet enables social movements that may not have existed or taken off before.)

"The internet has allowed people who supported legalization all along, and who felt alone, marginalized, and in the minority, to realize that there were millions of others who felt the same way," Angell of the Marijuana Majority said. "And it allowed them to collaborate in a way that wasn't possible before."

Sometimes the internet simply provided better information. Take Erowid, an online drug encyclopedia that simply catalogs research and users' experiences, with a focus on not purposely playing up or playing down any drugs' risks. The website's mission might seem like a standard or even boring concept today, but when it launched in 1995, Erowid was the only thorough, quick source for information on drug that wasn't laced with sensationalism and hyperbole.

"There was an enormous hole in terms of having basic information"

"When we started this project, it was obvious to us that there was a giant gap," Earth Erowid, who co-founded Erowid with his wife, Fire, told me. "There was an enormous hole in terms of having basic information."

"There was a lot of the 'just say no' rhetoric and the hyperbolic, anti-drug warnings out there about how everything was going to kill you," Fire added. "So there was definitely a field in which it was easier to do better."

Beyond making it much easier to look up basic information, the internet also made it much easier — and normal — for people to talk about drugs with the advent of social media. "When I was a college student around 1990, other than hardcore political wonky types … nobody really talked about drug legalization," Fabio Rojas, a professor at Indiana University who studies social movements, previously told me. "Now you can go on Facebook or Twitter or Instagram, and people can share a news story. You get exposed to it constantly."

The result: More people have a nuanced perspective about drugs — people generally acknowledge drugs carry some serious risks, but they also know that drugs can be beneficial or at least okay, even in recreational settings, for many people. And this has opened more people to the idea that maybe it's fine to let people legally use the less harmful substances that are currently illegal for recreational or medical purposes.

Marijuana is the obvious example. Over the past few years, younger Americans have increasingly expressed views that smoking marijuana does not carry great risk (which isn't completely right) — and now seven in 10 US adults, according to a survey by the Pew Research Center, say marijuana is less harmful to one's health than alcohol. At the same time, more Americans say they support marijuana legalization, and support for moving away from strict mandatory minimum sentences for drug crimes has increased, according to Pew.

Even without the internet, it's possible these public opinion shifts may have happened over time anyway — as Americans were faced with the costs and ineffectiveness of mass incarceration and the failures of the war on drugs. But the internet allowed these conversations to happen more freely, speeding up a political process that could have otherwise taken much longer.