This book examines social patterns in 2,000 mass shootings in the United States between 2013 through 2020. While mass shootings are often described as psychological, the authors show that there are social factors that produce the anger needed to commit a mass shooting. These factors are fairly common and can be addressed to stem the anger earlier. The factors include chronic poverty, sudden unemployment, relationship problems, domestic violence, social isolation, and alcohol. Common social strains can metastasize and be lethally dangerous. By understanding the social factors, we can reduce the anger and frustration people feel that would drive them to killing others.