The report found that half of the country's mass attacks from 2016 to 2020 were sparked by personal, domestic or workplace disputes.
Lina Alathari is Chief of the U.S. Secret Service National Threat Assessment Center.
"These were attackers retaliating for some sort of perceived wrongs that may have been related to either personal issues, domestic situations with partners, as well as workplace issues. But if you look at the top three, sort of 75% of attacks were carried out, mostly grievances but also then you see ideologically motivated attacks in which attackers were conducting an attack based on targeting a certain gender, race, or ethnic groups in line with some of the theories they had."
The 70-page report, issued on Wednesday, examined 173 incidents where three or more people were harmed.
The attacks targeted workplaces, schools, religious institutions and public transportation, among other locations, killing 513 people and injuring 1,234.
The attackers were overwhelmingly men, often with histories of mental health issues, financial insecurity or engaging in domestic violence. Guns were typically the weapon of choice.
Mass shootings have become a regular occurrence in the United States in recent decades, but lawmakers remain divided on the solutions, with Democrats calling for more gun control measures while Republicans focus on mental health and increased security.
The report comes days after a pair of mass shootings in California took the lives of 18 people and as authorities searched for motives in the attacks, both linked to older men.
