Mental imbalance. Poverty. Wild West syndrome. Alcoholism. Too many guns. All these factors and more have been seen for decades as causes of gun-related homicides in the United States, which has the most-armed civilian population in the world. Now police, government officials, criminologists, social workers and mental health experts are saying that last year a new factor helped fuel gun violence and gun sales－the pandemic. As the number of people in the US killed by COVID-19 approaches 400,000 and health officials try to vaccinate millions to stem the surge, the country has seen gun sales and related violence rise since the early stages of the pandemic.