An officer during the 2010 riots in Oakland, California, following the police shooting of Oscar Grant. (Photo: Thomas Hawk/Flickr)

Over the last few years, the streets of places like Ferguson have at times more closely resembled a military zone than they have an American city. That's in part because the police officers roaming those streets, donning camouflaged vests and wielding riot guns, are almost indistinguishable from American soldiers. Now, President Obama wants to throw the brakes on the militarization of America’s police.

During a visit to crime-wracked Camden, New Jersey, on Monday, Obama announced that his administration is seeking to ban the transfer of military equipment and weaponry—including “armored vehicles, bayonets, grenade launchers, ammunition of .50-caliber or higher and some types of camouflage uniforms,” the Washington Post reports—to civilian law enforcement agencies.

"We’ve seen how militarized gear sometimes gives people a feeling like they are an occupying force as opposed to a part of the community there to protect them," Obama said, referencing the events in Ferguson in 2014, as well as the more recent unrest in Baltimore. "Some equipment made for the battlefield is not appropriate for local police departments."

When you’re dressed for battle, everything starts to look like a war—including the citizens you’re supposedly there to protect and serve.

The Obama administration has public opinion on its side: Despite the fact that “law-and-order” politics remains a powerful tendril of American political life, a Huffington Post/YouGov poll taken following the events in Ferguson found that a plurality of Americans overwhelmingly opposed the use of military gear by local police, despite expressing general confidence in law enforcement.

But regardless of political expediency, psychological research suggests that demilitarization of law enforcement isn’t just a matter of making citizens feel warm and fuzzy: The presence of increasingly large and intimidating weapons may actually cause people to act violently.

The “weapons effect,” as psychologist Brad Bushman called it in Psychology Today, says that the mere presence of a weapon or the threat of violence can in turn make us ready for violence. The logic of weapons naturally escalating tensions applies on both sides of confrontation between police and a crowd. Either the flash of a knife in a crowd or the menacing stance of a riot policeman can send both cops and citizens into a social-psychological arms race. Psychologists Leonard Berkowitz and Anthony LePage established weapons as “aggression-eliciting stimuli” in a 1967 issue of the Journal of Personality and Social Psychology. “Guns not only permit violence, they can stimulate it as well,” Berkowitz explained. “The finger pulls the trigger, but the trigger may also be pulling the finger.”

This phenomenon doesn’t just occur in the lab. Bushman gives the example of an experiment in which a pick-up truck with a Confederate flag (the universal symbol for an antagonist in research experiments, apparently) would deliberately stall at a red light. The researchers then measured the honks of aggrieved motorists as indicators of frustration and hostility, depending on whether the truck had a .303-caliber military rifle in the gun rack on the back. “What is amazing about this study is that you would have to be pretty stupid to honk your horn at a driver with a military rifle in his truck—if you were thinking, that is,” Bushman writes. “But people were not thinking—they just naturally honked their horns after seeing the gun. The mere presence of a weapon automatically triggered aggression."

This, according to Obama, is a core obstacle for re-building trust between civilians and law enforcement. The police should be well-prepared for any crisis they face, but the presence of what look like military commandos marching down local Main Street has been proven, both scientifically and anecdotally, to be damaging to community policing. And as New York’s Jesse Singal pointed out in a series of interviews last year, criminologists and psychologists generally tend to agree that the more than $5 billion in equipment transferred from the military to local law enforcement since the 1990s is doing far more harm than good. After all, when you’re dressed for battle, everything starts to look like a war—including the citizens you’re supposedly there to protect and serve.