What explains U.S. mass shootings? The US has about the same rates of mental illnesses as other countries. There is almost no correlation between video games or racial diversity and gun violence. The big difference is ease of access to firearms and the vast number of firearms in circulation, at least 275 million.
Gun control legislation tends to reduce gun murders, according to an analysis of 130 studies from 10 countries.
International comparisons do suggest some answers https://nyti.ms/2hODjP5