Collective trauma

A collective trauma is a traumatic psychological effect shared by a group of people of any size, up to and including an entire society. Traumatic events witnessed by an entire society can stir up collective sentiment, often resulting in a shift in that society's culture and mass actions.

Well known collective traumas include: The John F. Kennedy assassination in the United States, the Estonia shipping disaster in Sweden, the September 11, 2001 attacks in the United States and various others.

Strategies for dealing with collective trauma
Collective traumas have been shown to play a key role in group identity formation (see: Law of Common Fate). During World War II, a US submarine, the USS Puffer (SS-268), came under several hours of depth charge attack by a Japanese surface vessel until the ship became convinced the submarine had somehow escaped. Psychological studies later showed that crewmen transferred to the submarine after the event were never accepted as part of the team. Later, US naval policy was changed so that after events of such psychological trauma, the crew would be dispersed to new assignments.