In recent weeks, as mass shootings across the United States dominated headlines, many Americans have observed that the country seems to be returning to something like a pre-pandemic state — shootings included.

But for all the ways in which gun violence is a distinctly American problem, the idea that killings are ramping up as people move back toward their usual routines isn’t necessarily unique.

Although the number of homicides sharply decreased in numerous countries during the early months of the coronavirus shutdown, “any significant changes were short-lived and pre-pandemic dynamics soon returned,” a recent research brief from the United Nations Office on Drugs and Crime concluded.

Analyzing monthly crime data from 21 countries, researchers found the majority did experience a significant drop in the number of homicide victims during March and April of 2020. By the summer, however, the number of victims was back to usual. That trend proved true in some European countries, including Italy and Spain, where homicides are more frequently linked to domestic violence, and in Latin American nations, including Colombia and Guatemala, where the rates are higher and often linked to organized crime.

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New Zealand, which was one of the first countries to be able to lift intensive coronavirus-related restrictions, may offer an illustrative example.

The number of victims reporting crime to the police decreased from 28,342 in January 2020 to 12,323 in April 2020, when shutdown restrictions were in place. “We’ve never seen crime drop like that, ever — not even in world wars. It was incredible,” Inspector Brent Register told the New Zealand Herald, noting the main cause for the drop was a decrease in burglaries as people switched to working from home.

Soon after restrictions were lifted, there was a flurry of activity: Last June, the paper reported “homicides appear to have spiked across New Zealand since Kiwis came out of lockdown,” during what it dubbed “Murderous May.”

But in the long run, the numbers evened out. Overall, crime in New Zealand was down 6.5 percent in 2020, which Register attributed to the fact that the country still has not fully returned to its normal rhythms.

“You’ve only got to walk downtown and there are fewer people,” he said.

As the U.N. report notes, there was plenty of reason to assume crime rates would fall as more people stayed home, making it harder to break into homes or seek out targets on the street. In other words, there would be fewer opportunities to commit crimes during the shutdown, but crime would return to regular levels as restrictions were eased.

But the “strain theory” of crime holds that crime levels are likely to rise in situations where a large share of the population comes under increased economic stress — as occurred worldwide during the pandemic as businesses closed and unemployment numbers ballooned. Operating under that assumption, the U.N. report points out, one could assume crime rates would spike during the shutdown but eventually fall to their pre-pandemic levels as life went back to normal.

Trying to figure out why gun violence increases or decreases during any given point in time tends to be tricky — in part because law enforcement statistics tend to lump together homicides carried out under vastly different circumstances, such as domestic violence, which has increased during the shutdown, and gang-related killings or hate crimes.

In some countries where homicide rates fell at the start of the pandemic, including Chile, Ecuador, El Salvador and Honduras, “it is difficult to unequivocally attribute such changes to the lockdown,” the U.N. report states. In the instance of El Salvador, for example, a government crackdown on gangs may have played a major role.

In the United States, gun violence never actually went away. “Gun violence has been higher than ever,” Champe Barton, a reporter tracking gun violence at the Trace, recently told PBS News Hour. “Even mass shootings, as defined by the Gun Violence Archive as more — four or more people injured or killed, not including the shooter, even those were up higher than they’d ever been.”

Because most of those incidents were the sort of “more routine gun deaths that happen as part of community conflicts in cities across the country,” Barton said, there’s a sense that mass shootings went away. In reality, they were still taking place in low-income neighborhoods — there just weren’t as many of the “lone-style shooter” attacks like the shooting that took place at a FedEx sorting facility in Indianapolis last week, which tend to draw the most attention.

“While COVID-related restrictions may have temporarily suppressed homicide rates, the pandemic has placed individuals and institutions under tremendous strain, ultimately pushing homicide rates higher,” a recent report from the National Commission on COVID-19 and Criminal Justice and Arnold Ventures noted.

The researchers observed the same pattern documented in the U.N. report: A decrease in homicides during the early months of the pandemic, followed by a return to normal or even higher-than-usual levels of violence.

In fact, many experts suggest reduced access to mental health services — and possible interventions — during the pandemic may have made matters even worse. “It could very well be a buildup of pent-up frustration by some emotionally disturbed people,” Mike Lawlor, an associate professor of criminal justice at the University of New Haven in Connecticut, recently told NBC News.

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