In the US, the justified use of deadly force by law enforcement must meet one of two legal requirements: it must either be to protect an officer’s life or the lives of others, or to prevent a suspect’s escape if the officer reasonably believes the suspect to be a public threat. In either case, it doesn’t matter whether the threat perceived by the officer is real, as long as the officer’s assessment of the threat is “objectively reasonable.” The legal standard for “reasonable belief” understandably gives a lot of credence to the officer’s snap judgment of who/what constitutes a threat. An overwhelming majority of justified police homicides in the US involved the presence, or the assumed presence, of a gun.

More people are killed by the police each day in America than are killed by police in most countries in a year. England and Wales averaged just over two police homicides per year over the past 24 years. Canada averages 25 per year. In the US meanwhile, the FBI recorded an average of 400.6 justifiable police homicides each year from 2008 to 2012. But the actual number is almost certainly considerably higher than that, because the FBI's statistics are voluntarily reported by individual departments, represent only a fraction of law enforcement agencies, and exclude police homicides deemed to have been unjustified. The disparity is huge regardless, even accounting for the demographic differences between countries.

It's not immediately clear why the number of police shootings in America remains so high. The tragedy in Dallas notwithstanding, policing in America has gotten progressively safer since the mid-1970s. And since 1992, violent crime has also declined consistently. Since the early 1990s however, the ratio of justified police homicides (that we know about) to violent crimes has steadily increased. As Philip Bump of the Washington Post observed last year, in 1991 there were 1.92 justified police homicides for every 10,000 violent crimes. In 2001, that ratio had risen to 2.63, and by 2012 it was 3.38. So even though violent crime is on a 20-year decline, and fewer officers are dying in the line of duty than at any time since the mid-1950s, the number of justified police killings appears to be holding steady, year after year.

So if American police officers aren't killing in response to external factors like rising violent crime rates or increased physical danger, is their sustained use of deadly force instead due to rising structural racism within their departments? Well, again, the data are mixed. A surprising new study by economist Roland Fryer Jr. of Harvard examines a large number of police shootings in 9 different American cities between 2000 and 2015, finding that while black men and women receive far worse treatment from law enforcement than whites overall, they are no more likely to be shot by police than are whites. This is a controversial finding, given that a number of other studies, including a survey of recent fatal police shootings by the Washington Post, suggest that Black Americans are "up to 2.5 times" more likely to be shot and killed by police than whites. Regardless, Fryer's study supports the main argument of the Black Lives Matter movement. American police barely even have to explain the use of non-lethal force, and they use it both casually and systemically against people of color at a rate far out of proportion to their numbers.

Another inarguable fact: American police are as jumpy on the trigger as ever. Maybe that's because the public they serve-white, black, Latino and otherwise-is absolutely awash in an unprecedented number of guns. Beginning in 2009, in response to fears that the Obama administration might restrict gun sales, gun manufacturers began massively ramping up the production and sale of their products, pumping an unprecedented number of firearms into American homes and streets. In 2013, US gun manufacturers produced a staggering 10.9 million guns-almost 3 times more guns than had been produced on average each year between 1986 and 2008.

We have only a rough sense of how many guns are out there, of what type, and how they're used, because gun manufacturers have deployed the NRA to choke off most funding and data sources for credible firearm epidemiology. But we do know that there are roughly 300 million guns of various kinds currently in circulation--approximately one for every American. Which is comparable to the number of personal computers. You are surrounded by guns right now. As are the police.

Numbers like these mean that almost any police shooting can be justified by the reasonable fear of a firearm-even the killing of a 12 year old boy holding a bb gun. The ubiquity of essentially unregulated guns, coupled with a legal standard requiring only that an officer reasonably fear for their safety in order to justify the use deadly force, effectively gives American police unfettered license to kill, under color of law.

Aside from all of the other problems that accompany an over-armed society, the sheer pervasiveness of guns harms the relationship between the police and the public. It makes every public interaction with police more dangerous than it needs to be, even if nothing happens. It feeds the frightening undercurrents of authoritarianism and militarization within the ranks of American law enforcement. And all too often, it excuses what would, in any other context, be called murder.

In a year, maybe two, some panicked cop somewhere will shoot and kill a toddler holding a toy gun in his front yard, under the mistaken assumption that the toy was a real, loaded pistol he’d taken from his mother’s purse. And in accordance with the perverse logic of our gun-mad culture, a grand jury will pronounce it tragic, but justified.