It was just another video game tournament. Based on the live stream, players were playing Madden NFL 19, and shoutcasters were giving the typical play-by-play, while the chat on Twitch.tv carried on with conversation about the match and memes. But then, a laser point appeared on one of the player’s chests.

Suddenly, 12 shots rang out. There was chaos on the live stream — screaming and running around as the game abruptly paused. A voice could be heard asking, “Oh, fuck, what’d he shoot me with?”

At that moment, this tournament in Jacksonville Landing in Florida, had become the site of another mass shooting in America. By the end of the gunfire, three people, including the shooter, were killed, and at least 11 were injured. It was a horrifying end to a tournament that was supposed to be a qualifying event for a national competition sponsored by EA Sports later this year.

By now, mass shootings have become almost routine in America. One seems to make the news every month or so. Since the mass shooting in Sandy Hook Elementary School in 2012, more than 1,800 mass shootings — defined as any shooting in which four or more people, excluding the shooter, were shot although not necessarily killed — have happened in the US.

We don’t yet know why this particular shooter carried out a horrific act of gun violence. But we do know why this keeps happening in America.

Guns. America has the laxest gun laws of any wealthy country in the world, and it also has by far the highest number of privately owned firearms. The easy access to guns makes it easy for anyone to escalate just about any encounter into deadly violence. This means not just more mass shootings, but gun violence in general, which the US has a lot more of than its developed peers.

The US can do something about this. But to understand that, it’s crucial to grasp five key points about America’s gun problem, from how unique it is to why it might take more far-reaching solutions than anyone is proposing in mainstream politics.

1) America has a unique gun violence problem

The US is unique in two key — and related — ways when it comes to guns: It has way more gun deaths than other developed nations, and it has far higher levels of gun ownership than any other country in the world.

The US has nearly six times the gun homicide rate of Canada, more than seven times that of Sweden, and nearly 16 times that of Germany, according to United Nations data compiled by the Guardian. (These gun deaths are a big reason America has a much higher overall homicide rate, which includes non-gun deaths, than other developed nations.)

Mass shootings actually make up a small fraction of America’s gun deaths, constituting less than 2 percent of such deaths in 2016. But America does see a lot of these horrific events: According to CNN, “The US makes up less than 5% of the world’s population, but holds 31% of global mass shooters.”

The US also has by far the highest number of privately owned guns in the world. Estimated for 2017, the number of civilian-owned firearms in the US was 120.5 guns per 100 residents, meaning there were more firearms than people. The world’s second-ranked country was Yemen, a quasi-failed state torn by civil war, where there were 52.8 guns per 100 residents, according to an analysis from the Small Arms Survey.

Another way of looking at that: Americans make up less than 5 percent of the world’s population, yet they own roughly 45 percent of all the world’s privately held firearms.

These two facts — on gun deaths and firearm ownership — are related. The research, compiled by the Harvard School of Public Health’s Injury Control Research Center, is pretty clear: After controlling for variables such as socioeconomic factors and other crime, places with more guns have more gun deaths. Researchers have found this to be true not just with homicides, but also with suicides (which in recent years were around 60 percent of US gun deaths), domestic violence, and even violence against police.

For example, a 2013 study, led by a Boston University School of Public Health researcher, found that, after controlling for multiple variables, each percentage point increase in gun ownership correlated with a roughly 0.9 percent rise in the firearm homicide rate.

This chart, based on data from GunPolicy.org, shows the correlation between the number of guns and gun deaths (including homicides and suicides) among wealthier nations:

Guns are not the only contributor to violence. (Other factors include, for example, poverty, urbanization, and alcohol consumption.) But when researchers control for other confounding variables, they have found time and time again that America’s high levels of gun ownership are a major reason the US is so much worse in terms of gun violence than its developed peers.

2) The problem is guns, not mental illness

Supporters of gun rights look at America’s high levels of gun violence and argue that guns are not the problem. They point to other issues, from violence in video games and movies to the supposed breakdown of the traditional family.

Most recently, they’ve blamed mental health issues for mass shootings.

But as far as homicides go, people with mental illnesses are more likely to be victims, not perpetrators, of violence. And Michael Stone, a psychiatrist at Columbia University who maintains a database of mass shooters, wrote in a 2015 analysis that only 52 out of the 235 killers in the database, or about 22 percent, had mental illnesses. “The mentally ill should not bear the burden of being regarded as the ‘chief’ perpetrators of mass murder,” he concluded. Other research has backed this up.

More broadly, America does not have a monopoly on mental illness. That’s not to say more access to mental health care wouldn’t help; it could, for example, be effective for reducing the number of gun suicides. But mental health issues aren’t what make the US stand out in terms of gun violence.

The problem that’s unique to the US, instead, is guns — and America’s abundance of them.

As a breakthrough analysis by UC Berkeley’s Franklin Zimring and Gordon Hawkins in the 1990s found, it’s not even that the US has more crime than other developed countries. This chart, based on data from Jeffrey Swanson at Duke University, shows that the US is not an outlier when it comes to overall crime:

Instead, the US appears to have more lethal violence — and that’s driven in large part by the prevalence of guns.

”A series of specific comparisons of the death rates from property crime and assault in New York City and London show how enormous differences in death risk can be explained even while general patterns are similar,” Zimring and Hawkins wrote. “A preference for crimes of personal force and the willingness and ability to use guns in robbery make similar levels of property crime 54 times as deadly in New York City as in London.”

This is in many ways intuitive: People of every country get into arguments and fights with friends, family, and peers. But in the US, it’s much more likely that someone will get angry at an argument and be able to pull out a gun and kill someone.

3) The research shows that gun control works

The research also suggests that gun control can work. A 2016 review of 130 studies in 10 countries, published in Epidemiologic Reviews, found that new legal restrictions on owning and purchasing guns tended to be followed by a drop in gun violence — a strong indicator that restricting access to firearms can save lives.

Consider Australia’s example.

In 1996, a 28-year-old man armed with a semiautomatic rifle went on a rampage in Port Arthur, Australia, killing 35 people and wounding 23 more. It was the worst mass shooting in Australia’s history.

Australian lawmakers responded with legislation that, among other provisions, banned certain types of firearms, such as automatic and semiautomatic rifles and shotguns. The Australian government confiscated 650,000 of these guns through a mandatory buyback program, in which it purchased firearms from gun owners. It established a registry of all guns owned in the country and required a permit for all new firearm purchases. (This is much further than bills typically proposed in the US, which almost never make a serious attempt to immediately reduce the number of guns in the country.)

Australia’s firearm homicide rate dropped by about 42 percent in the seven years after the law passed, and its firearm suicide rate fell by 57 percent, according to a review of the evidence by Harvard researchers.

It’s difficult to know for sure how much of the drop in homicides and suicides was caused specifically by the gun buyback program and other legal changes. Australia’s gun deaths, for one, were already declining before the law passed. But researchers David Hemenway and Mary Vriniotis argue that the gun buyback program very likely played a role: “First, the drop in firearm deaths was largest among the type of firearms most affected by the buyback. Second, firearm deaths in states with higher buyback rates per capita fell proportionately more than in states with lower buyback rates.”

One study of the program, by Australian researchers, found that buying back 3,500 guns per 100,000 people correlated with up to a 50 percent drop in firearm homicides and a 74 percent drop in gun suicides. As Dylan Matthews explained for Vox, the drop in homicides wasn’t statistically significant because Australia already had a pretty low number of murders. But the drop in suicides most definitely was — and the results are striking.

One other fact, noted by Hemenway and Vriniotis in 2011: “While 13 gun massacres (the killing of 4 or more people at one time) occurred in Australia in the 18 years before the [Australia gun control law], resulting in more than one hundred deaths, in the 14 following years (and up to the present), there were no gun massacres.”

4) State and local actions are not enough

A common counterpoint to the evidence on gun control: If it works so well, why does Chicago have so much gun violence despite having some of the strictest gun policies in the US?

White House press secretary Sarah Huckabee Sanders made this argument after the 2017 Las Vegas mass shooting: “I think if you look to Chicago, where you had over 4,000 victims of gun-related crimes last year, they have the strictest gun laws in the country. That certainly hasn’t helped there.”

It’s true that Chicago has fairly strict gun laws (although not the strictest). And it’s true that the city has fairly high levels of gun violence (although also not the worst in the US).

This doesn’t, however, expose the failure of gun control altogether, but rather the limits of leaving gun policies to a patchwork of local and state laws. The basic problem: If a city or state passes strict gun control measures, people can simply cross a border to buy guns in a jurisdiction with laxer laws.

Chicago, for example, requires a Firearm Owners Identification card, a background check, a three-day waiting period, and documentation for all firearm sales. But Indiana, across the border, doesn’t require any of this for purchases between two private individuals (including those at gun shows and those who meet through the internet), allowing even someone with a criminal record to buy a firearm without passing a background check or submitting paperwork recording the sale.

So someone from Chicago can drive across the border — to Indiana or to other places with lax gun laws — and buy a gun without any of the big legal hurdles he would face at home. Then that person can resell or give guns to others in Chicago, or keep them, leaving no paper trail behind. (This is illegal trafficking under federal law, but Indiana’s lax laws and enforcement — particularly the lack of a paper trail — make it virtually impossible to catch someone until a gun is used in a crime.)

The result: According to a 2014 report from the Chicago Police Department, nearly 60 percent of the guns in crime scenes that were recovered and traced between 2009 and 2013 came from outside the state. About 19 percent came from Indiana — making it the most common state of origin for guns besides Illinois.

This isn’t exclusive to Chicago. A 2016 report from the New York State Office of the Attorney General found that 74 percent of guns used in crimes in New York between 2010 and 2015 came from states with lax gun laws. (The gun trafficking chain from Southern states with weak gun laws to New York is so well-known it even has a name: “the Iron Pipeline.”) And another 2016 report from the US Government Accountability Office found that most of the guns — as many as 70 percent — used in crimes in Mexico, which has strict gun laws, can be traced back to the US, which has generally weaker gun laws.

That doesn’t mean the stricter gun laws in Chicago, New York, or any other jurisdiction have no effect, but it does limit how far these local and state measures can go, since the root of the problem lies in other places’ laws. The only way the pipeline could be stopped would be if all states individually strengthened their gun laws at once — or, more realistically, if the federal government passed a law that enforces stricter rules across the US.

5) America probably needs to go further than anyone wants to admit

America’s attention to gun control often focuses on a few specific measures: universal background checks, restrictions on people with mental illnesses buying firearms, and an assault weapons ban, for example. It is rare that American politicians, even on the left, go much further than that. Something like Australia’s law — which amounts to a confiscation program — is never seriously considered.

As Matthews previously explained, this is a big issue. The US’s gun problem is so dire that it arguably needs solutions that go way further than what we typically see in mainstream proposals — at least, if the US ever hopes to get down to European levels of gun violence.

If the fundamental problem is that America has far too many guns, then policies need to cut the number of guns in circulation right now to seriously reduce the number of gun deaths. Background checks and other restrictions on who can buy a gun can’t achieve that in the short term. What America likely needs, then, is something more like Australia’s mandatory buyback program — essentially, a gun confiscation scheme — paired with a serious ban on specific firearms (including, potentially, all semiautomatic weapons).

But no one in Congress is seriously proposing something that sweeping. The Manchin-Toomey bill, the only gun legislation in Congress after Sandy Hook that came close to becoming law, didn’t even establish universal background checks. Recent proposals have been even milder, taking small steps like banning bump stocks or very slightly improving the existing system for background checks.

Part of the holdup is the Second Amendment. While there is reasonable scholarly debate about whether the Second Amendment actually protects all Americans’ individual right to bear arms and prohibits stricter forms of gun control, the reality is the Supreme Court and US lawmakers — backed by the powerful gun lobby, particularly the NRA — widely agree that the Second Amendment does put barriers on how far restrictions can go. That would likely rule out anything like the Australian policy response short of a court reinterpretation or a repeal of the Second Amendment, neither of which seems likely.

So the US, for political, cultural, and legal reasons, seems to be unable to take the action that it really needs.

None of that is to say that milder measures are useless. Connecticut’s law requiring handgun purchasers to first pass a background check and obtain a license, for example, was followed by a 40 percent drop in gun homicides and a 15 percent reduction in handgun suicides. Similar results — in the reverse — were reported in Missouri when it repealed its own permit-to-purchase law. It’s difficult to separate these changes from long-term trends (especially since gun homicides have generally been on the decline for decades now), but a review of the evidence by RAND linked milder gun control measures, including background checks, to reduced injuries and deaths — and that means these measures likely save lives.

There are also some evidence-based policies that could help outside the realm of gun control, including more stringent regulations and taxes on alcohol, changes in policing, and behavioral intervention programs.

But if America wants to get to the levels of gun deaths that its European peers report, it will likely need to go much, much further on guns in particular.