Mind Control

The Milgram Experiments proved that ordinary people will follow orders up to and including murder, so long as they perceive that it comes from an apparent authority.
Many governments in the 20th Century devoted untold hours and billions of dollars to the study of mind control to be used for spying and assassinations.
How far will humans go to test the limits of what can be done to their fellow man? What does (recent) History show in this regard?