On Saturday, Michael Pimentel, the chief of police in the small town of Elmendorf, Texas — population: 1,500 — made what seemed to be a routine traffic stop. But moments after pulling over the vehicle, there was a brief struggle, during which Pimentel was hit with “multiple gunshots.” He was airlifted to an area hospital, where he later succumbed to his wounds.

According to police, the suspected shooter, 24-year-old Joshua Manuel Lopez, was wanted on a misdemeanor warrant for graffiti.

Incidents like this one aren’t an everyday occurrence in America, but neither are they exceedingly rare. According to the Texas Department of Public Safety, Pimentel was the fifth law enforcement officer to die in the line of duty this year in the Lone Star State.

Police violence in America differs from that of other wealthy democracies in two important ways. First, police in the US kill exponentially more citizens than they do in other countries. The other salient fact is that exponentially more American police are killed in the line of duty than their colleagues abroad.

According to an analysis of FBI data by USA Today, at least 400 Americans are killed by police every year. But that’s a low-ball figure: “The killings are self-reported by law enforcement and not all police departments participate so the database undercounts the actual number of deaths. Plus, the numbers are not audited after they are submitted to the FBI and the statistics on ‘justifiable’ homicides have conflicted with independent measures of fatalities at the hands of police.”

In 2011, police in England and Wales, Australia and Germany — countries with a combined population of 150 million and strict gun control laws — police killed just 14 people. German police fired a total of 85 bullets away from the shooting range that year — 49 of them warning shots. In 2013, Icelandic police shot and killed a suspect for the first time in the nation’s history.

But police in those countries aren’t dealing with a heavily armed citizenry, some of whom regard their government as an enemy of the people.

According to the International Small Arms Survey, the US has the highest rate of private gun ownership in the world — about a third higher than Yemen, which holds the number two spot. As Adam Winkler, a professor of law at UCLA, wrote last week, we shouldn’t “fail to recognize the profound impact this has on law enforcement.”

Because there are so many guns out there, police officers are trained to live in fear of the very people they are supposed to protect and serve. Anytime a police officer pulls over a car, he or she must worry that the person inside that car will have a gun that could be turned on them. At training academies throughout the nation, new recruits are taught that cop-killers need two things: a will to kill and an opportunity to act.

It’s not just the raw number of guns in the US, but our culture of gun worship and lack of sufficient regulation — in part, the result of the gun lobby’s ubiquitous arguments that firearms are the last bulwark against tyranny, and should be carried by everyone, virtually everywhere.

In 2012, 127 American cops were killed in the line of duty; that’s around the number of Canadian officers killed in the 48-year period between 1961 and 2009. And a total of three British police were killed in 2012 — ending a four-year streak in which no police officers were victims of intentional murder (one died when he was thrown from a vehicle during a high-speed chase).

There are a number of reasons why American police seem more likely to use their guns than those in other countries. Race plays a role. The US isn’t the most racist country in the world, but in the developed world, we are one of the most ethnically diverse.

As Rebecca Leber reported for The New Republic, “Social science research shows that, in video simulations, people are more likely to shoot black men.”

The participants—often undergraduate students, both black and white—play a simulation where they press “shoot” if they think the white or black suspect holds a gun. Consistently, psychologists have found the students more likely to shoot the unarmed black person over an unarmed white person.

The militarization of domestic law enforcement is a factor, with heavily-armed SWAT teams breaking down doors to arrest people suspected of even non-violent offenses like credit card fraud. And then there is the growing influence of a military mindset in domestic law enforcement, as tens of thousands of veterans returning to civilian life seek jobs in law enforcement; according to one estimate, 80 percent of the Dallas Police Department’s hires over a two-year period were military vets, and around 20 percent of LAPD officers now have military backgrounds.

We’ve also framed drug enforcement as a “war,” and police often approach it that way. With one of the highest rates of poverty and inequality among the high-income countries, the US also has pockets of highly concentrated destitution and hopelessness that breed crime and violence.

But there’s another angle to this story as well: The US features a unique and toxic mix of gun culture and militant anti-governmentalism. As a result, police officers aren’t entirely wrong to believe that they’re operating in a potential combat zone.

Although motor vehicle accidents are the leading cause of death for cops on the beat, an average of 57 police officers were killed with guns in the US annually between 2001 and 2010; of the 17 members of law enforcement killed in Ireland since the end of “The Troubles” in 1998, only two were gunshot victims (one in a case of friendly-fire).

Fifty-seven may seem a relatively small number in a country of over 300 million, but many more officers are wounded or fired upon (there are no nationwide statistics for these lesser incidents of gun violence).

Police in the US also face a unique challenge — and singular threat — from anti-government extremists. No other police force in a functional democracy has experienced something like the Bundy Ranch standoff in Nevada in April, where federal agents found themselves outgunned by heavily-armed militias — which included well-trained military veterans — holding the strategic high ground.

As the Southern Poverty Law Center noted last week, a new report from the Department of Homeland Security found that, “after years of sporadic violence from domestic extremists motivated by antigovernment ideologies, there has been ‘a spike within the past year in violence committed by militia extremists and lone offenders who hold violent anti-government beliefs.'” Last month, a survey of 364 officials from 175 law enforcement agencies conducted by the National Consortium for the Study of Terrorism and Response to Terrorism (START) found that members of the Sovereign Citizens movement are now considered to be the greatest terrorist threat faced by law enforcement. Third on the list, after Islamic extremists, were members of militia and “patriot” groups.

Since 2002, Sovereign Citizens have killed at least ten members of law enforcement, and failed in a number of other attempts, including two potentially deadly incidents in the past three months alone. And while most are nonviolent, with an estimated 300,000 members of the Sovereign Citizens in the US, only a fraction need to take up arms and target law enforcement to constitute a danger to the police.

None of this excuses overly aggressive policing or reflexively absolves cops who kill. It’s implicit in the social contract that law enforcement officers have to take risks in order to protect and serve. But it’s hard to deny that these factors play a role in many police feeling that they’re patrolling a war zone. And there’s little question that, considering the combination of all of these dynamics, along with racial animus and the militarization of police, we have a serious problem.