This doesn't mean that all men, in the U.S. or anywhere else, believe that their masculine value is in their ability to be aggressive or exert physical force. But as a rule, men are exposed to and subjected to these cultural values, and many people expect them to measure up to them. According to many researchers, these expectations play into why violence and masculinity are so deeply linked in our culture.

"Men who feel 'unmanned' will exaggerate their height, number of past sexual partners, and other stereotypical markers of 'manliness'—this confusion and fear about their perceived status or power is a driving force behind a lot of male violence."

It's been a long-standing argument that men are more violent because they're "reinforcing" their power at the top of the cultural totem pole in patriarchal situations. But thinkers today are challenging that. Specialist on masculine violence Dr. Michael Kimmel declared in his 2007 essay “Contextualizing Men’s Violence: The Personal Meets the Political" that masculinity is not "the experience of power; it is the experience of entitlement to that power." And Michael Kaufman noted in his ground-breaking 1999 essay "The Seven P's of Male Violence," "Although maleness and masculinity are highly valued, men are everywhere unsure of their own masculinity and maleness, whether consciously or not."

Sometimes, the behavior produced when men scramble to recover threatened masculinity can be relatively harmless — the research of Professor Benoit Monin, in studies published in Social Behavior in 2015, found that men who feel "unmanned" will exaggerate their height, number of past sexual partners, and other stereotypical markers of "manliness." However, the dark side is obvious —this confusion and fear about their perceived status or power is a driving force behind a lot of male violence. In a 2016 series of interviews with American men, published in the Journal of Interpersonal Violence, the study authors concluded that "violence was viewed as necessary in particular situations to assert or maintain one’s social status and sense of self as masculine when faced with threats to manhood status."

This belief can be seen in cases like that of Elliot Rodger, whose mass shooting in Isla Vista in 2014 was, according to his writings, partially motivated by his feelings about perceived lack of female desire for him. "I don't know why you girls aren't attracted to me, but I will punish you all for it," he said in a video shot before the massacre.

Tara Tober and Tristan Bridges of the University of California, Santa Barbara, authored an influential piece of research in 2015 about the link between American masculinity and mass shootings; after analyzing studies about what fuels male violence, they wrote "The research does not suggest that men are somehow inherently more violent than women. Rather, it suggests that men are likely to turn to violence when they perceive themselves to be otherwise unable to stake a claim to a masculine gender identity."

A 2016 study bore this theory out — according to a report in Pacific Standard, researchers found that the stress a particular man felt regarding the discrepancy between "how masculine [he] feels, and how that self-image stacks up against societal expectations" was an indicator of potential for violence. While men who felt that they comfortably embodied "masculine norms" were the group most likely to have committed violence, men "who consider themselves less than truly masculine, and who feel tense or anxious as a result of that nagging perception" were also likely to act violently — these men who were anxious about their own masculinity "reported rates of assaults causing injury 348 percent higher than men low on discrepancy stress."

It's worth noting that a staggering number of men who go on to engage in mass violence have backgrounds filled with domestic abuse. A 2017 report showed that one quarter of the men who had committed lethal violence with a political motivation since 2001 had been accused of domestic violence or sexual crimes in the past, and anti-gun violence group Everytown found that 16 percent of mass shooters from 2009 to 2015 had been charged with domestic violence prior to their shooting — a group that includes people from Pulse shooter Omar Mateen to Virginia Tech shooter Seung-Hui Cho to Congressional shooter James Hodgkinson to Planned Parenthood shooter Robert Lewis Dear. Charlottesville's James A. Fields purportedly engaged in domestic violence against his mother, too.