One of the most famous tales of World War I began when a fantasy fiction writer wrote a story in 1914 about British soldiers crying for help while facing overwhelming German forces near Mons, in France.

Their prayers summoned heavenly hosts of archers attacking the "heathen horde."

Soon, veterans started claiming that they saw these "angels" with their own eyes. Images of the Angel of Mons began appearing -- as fact -- in posters, paintings and popular songs.

It's hard to imagine a world in which nations led by rational, scientific elites could embrace these claims, said historian Philip Jenkins, in recent lectures at King University in Bristol, Tenn. That world is impossible to imagine because it was swept away a century ago by waves of change that few saw coming.

"What happened in the victory? 'Oh, angels appeared. The dead arose to fight for us.' When the Germans launched their great offensive in 1918, of course, what else could it be called? It's Operation Michael, after the leading archangel -- who by this point has become something like a German war god," said Jenkins, a distinguished professor at Baylor University and author of 27 books.

"If you look at the propaganda of the time, the assumption is that Christ is absolutely with US -- whoever WE are, the Germans, the Americans, whatever."

Before World War I, most global leaders followed a radically different set of assumptions, with ironclad ties between their governments and major religious institutions, he said. Many soldiers believed that St. Michael the Archangel, the Virgin Mary, even Joan of Arc, would fight by their side. As the war began, Germany experienced fervor many called a "New Pentecost," with Martin Luther as a messianic figure.

While it's common to believe that religion evolves slowly over time, in a linear manner, the evidence suggests that history lurches through periods of "extreme, rapid, revolutionary change, when everything is shaken and thrown up into the air," said Jenkins. Ever 50 years or so, new patterns and cultural norms seem to appear that never could have been predicted.