The United States as twice as many mass killings than any other country in the world. In 2018, there were 18 mass killings in one year. Many critics say it is the accessibility of guns in the United States that is the cause of the mass killings. But guns have always been available in the US, particularly since 1781, when the second amendment was passed granting citizens the right to own guns. But mass killing began to multiply at the end of the 20th Century and continued to do so into the 21st Century. People kill not because they have guns, but because they have an urge to kill. The urge to kill is brought on either by an emotional disturbance or a cultural disturbance or both. The urge to kill many people is brought on by an even greater disturbance. Mass killers are the products of dysfunctional families and dysfunctional cultures. The traumas of childhood and the frustrations of living in a dysfunctional culture lead to the eruptions of mass killings. This book probes the minds of mass killers and the meaning of their killings. It begins with an introduction to the psychology of mass killings, then offers six case histories of some of the most notorious mass killers in recent American history. It ends with a chapter on how to prevent mass killings.