The War of the Worlds hoax was effective at fooling audiences because it created mass hysteria.
Mass hysteria, also known as collective delusions, is defined as "the spontaneous, rapid spread of false or exaggerated beliefs within a population at large, temporarily affecting a particular region, culture or country."(8)
The type of hysteria that occurred with The War of The Worlds broadcast is called anxiety hysteria. This phenomenon is triggered by a person's perception of a threatening force and usually only lasts about a day.(8)
Many factors contribute to mass hysteria and collective delusions:
