This second book on genocide by Arthur Grenke marks an important change in the forces contributing to genocide. Prior to the Russian Revolution acts of genocide were usually committed on the conquered by the conquerors. However, after 1917 the Soviets and later the Nazis initiated programs of mass genocide and set the framework for later genocides that followed during the late 20th century. Victims of genocide were often designated as targets to be destroyed for political, ethnic, religious, and pseudo-scientific reasons. By eliminating the perceived internal threat, those who committed genocide did so with the perception they were creating an idealized society. This study, therefore, provides a comprehensive examination of the different cases of genocide and why genocide was committed during the 20th century. This book concludes by offering measures to prevent future acts of genocide.