“When we study the history of humanity we realize that the intensity and severity of human violence and aggression has increased over the centuries. Only in the 20th century millions of humans have been killed by other humans by pre-meditated murder, including the use of nuclear weapons.  If we review human murders we can classify them into the seven groups based on emotional, social, religious, economic or political motivation.”

DrK.Sohail (http://www.drsohail.com/essays.aspx/essays/seven_reasons_to_kill)