[In-group exclusivism has] killed more human beings and destroyed more cities and villages than all the epidemics, hurricanes, storms, floods, earthquakes, and volcanic eruptions taken together. It has brought upon mankind more suffering than any other catastrophe.

Sorokin (1954) http://books.google.nl/books?id=DGCleCxTkbIC The Ways and Power of Love. p. 461; As cited in: "[ Altruistic Love]" on what-when-how: In Depth Tutorials and Information