Police officers in the US shoot and kill hundreds of people each year, according to the FBI’s very limited data — far more than other developed countries like the UK, Japan, and Germany, where police officers might go an entire year without killing more than a dozen people or even anyone at all.

The Economist charted the differences in annual police shooting deaths in the US, UK, Japan, and Germany:

One explanation for the disparity is that murder and gun violence are more common in the US, putting police in more situations in which the use of force is necessary. A study in JAMA found that the US rate of gun deaths, which includes homicides and suicides, was 10.6 per 100,000 people in 2016. That dwarfed comparable developed nations: Switzerland’s rate was 2.8, Canada’s was 2.1, Australia’s was 1, Germany’s was 0.9, the United Kingdom’s was 0.3, and Japan’s was 0.2.

But why does the US have more homicides and gun violence than other developed countries?

One explanation: Americans are much more likely to own guns than their peers around the world. This means that conflicts — not just between police and civilians but between civilians — are more likely to escalate into deadly, violent encounters. The research bears this out: More guns lead to more gun violence. And for police in particular, one study in the American Journal of Public Health found that every 10 percent increase in firearm ownership correlated with 10 additional officers killed at the state level over a 15-year period.

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.

This is a result of cultural and policy decisions made by the US that have made firearms far more available in America than most of the world. For American police officers, this means they not only will encounter more guns, but they expect to encounter more guns, making them more likely to anticipate and perceive a threat and use deadly force as a result. And there is, in fact, a correlation between the number of guns and killings by police.

But deadly police encounters have drawn increased criticism over the past few years as cops have shot and killed unarmed or otherwise innocent black men and boys, highlighting the troubling racial disparities in how police use force.

For critics of law enforcement, the disparities indicate that it’s not just greater rates of gun ownership and violent crime that explain the higher number of police shootings in the US. Perhaps it’s the lax legal standards that allow cops to justify deadly force against suspects who pose no danger, and sometimes are only perceived to pose a threat to officers because cops hold racial biases that are endemic in the criminal justice system.