According to the Text, What Is "The Eighty Percent Rule

According to the text, what is "the eighty percent rule"?

A) The belief that 80% of people would accept or participate in acts of violence
B) The belief that 80% of wars are unnecessary
C) The idea that in modern wars 80% of deaths will be among civilians
D) The idea that 80% of soldiers who see combat will suffer post-traumatic stress disorder