The motivations of men who commit mass shootings are often muddled, complex or unknown. But one common thread that connects many of them - other than access to powerful firearms - is a history of hating women, assaulting wives, girlfriends and female family members, or sharing misogynistic views online, researchers say. Shannon Watts, the founder of Moms Demand Action for Gun Sense in America, cited a statistic that belies the sense that mass shootings are usually random: In more than half of all mass shootings in the United States from 2009 to 2017, an intimate partner or family member of the perpetrator was among the victims. "Most mass shootings are rooted in domestic violence," Ms. Watts said. "Most mass shooters have a history of domestic or family violence in their background. It's an important red flag." The plagues of domestic violence and mass shootings in the United States are closely intertwined. Psychiatrists [say that] the common argument that mental illness is the explanation for these massacres cannot explain the link between misogyny and mass shootings. Misogyny - or other types of hatred - is not necessarily a diagnosable mental illness. Instead, said Amy Barnhorst ... at the University of California, Davis, who has studied mass shootings, what ties together many of the perpetrators is "this entitlement, this envy of others, this feeling that they deserve something that the world is not giving them. And they are angry at others that they see are getting it."