Psychological propaganda used in war is as old as war itself. Psyching out the enemy in order to demoralize him is a handy way to pave the way for an easier victory.
A wise commander will attempt to minimize the other side’s psych warfare and maximize one’s own efforts.
One example I thought of off the top of my head involves the Roman Legions. As a rule the Gaul and Germanic warriors the Legions faced were larger than the average Roman soldier. Add to that their overall fearsome appearance and you may have a significant psychological edge in combat.
Roman Generals understood the concept and so emphasized the Roman advantages of a highly disciplined force that fought in coherent units rather than the individualistic style of the Gauls and Germans. An emphasis on teamwork and discipline thereby negated the psychological edge the larger, more powerful warriors might have enjoyed. As long as the Romans could maintain their formations and discipline they rarely lost, thereby gaining a psychological edge over their opponents.
Things have evolved since the days of Rome and now technology can play an even larger role in psyching out an enemy. Trick or Treat-The Strange Tale of Ghost Tape No. 10 is an excellent example derived from the Vietnam War. It’s a true “ghost story” for Halloween from NH Mallet’s blog.