When the Mercury Theatre group presented its production of H.G. Welles' War of the Worlds over the radio on the evening of October 30, 1938, the American public was particularly susceptible to mass panic disorder.  Developments in Europe -- the rise of Nazi Germany and its military actions against neighboring countries, and of Imperial Japan -- combined with fear of Communism emanating from Russia and the memories of the worst of the Great Depression still fresh, the stage was set for the massive misinterpretation of a radio broadcast purportedly reporting the invasion of the United States by an alien species.  

Given the right psychological atmosphere, usually stemming from major and traumatic international or domestic events, the public is susceptible to the kind of mass hysteria that resulted from the broadcast of War of the Worlds.  During the mid-1980s, when the Reagan Administration was conducting a psychological and actual war with the dictatorial regime of Muammar Qhaddafi in Libya, reports of the dispatch of Libyan terrorist "hit teams" to assassinate Americans resulted in wide-spread fear of terrorism on American shores.  The actual terrorist attacks by al Qaeda on New York City, the Pentagon, and the intended attack on the U.S. Capitol (the aircraft that crashed in Pennsylvania is believed to have been headed for either the Capitol or the White House, with best estimates indicating the Capitol), created precisely the type of climate in which the mass hysteria that occured in 1938 with a bogus radio broadcast could again occur.  Fear of the unknown, if provoked at the right time, can create panic.

The United States, of course, is not the only country susceptible to mass hysteria on the basis of rumor or deceit.  Violent riots are known to break out in Islamic countries upon rumors of anti-Muslim provocations.  The most alarming and devastating incident of mass hysteria having extremely unfortunate consequences was the fear among the German population that was stoked and exploited by Adolf Hitler.  By the time his regime came to an end, some ten million people had been murdered by the Nazis and their followers -- all because of rumor, inneundo, and prejudices little different than those necessary to create panic in most countries.

The kind of "doom" story most likely to trigger panic is one that is carefully tailored to exploit preexisting fears or prejudices.  In the current era, that involves fears of terrorism and of terrorist or criminal use of chemical or biological agents.  Films like "Outbreak," "Twelve Monkeys," and the book and movie "The Andromeda Strain" can increase peoples' fear of plague, resulting in panic and runs on supermarket supplies.  

To the extent that people have around-the-clock sources of information, it is harder to facilitate mass hysteria, at least in more socially-advanced countries.  All peoples, however, are vulnerable to having their emotions manipulated by a gifted storyteller.  Fears of terrorism, of infectious diseases, of foreign ideologies or religions, all provide the basis for mass entertainment than can cause equally large anxiety.