The reign of King Louis Philippe, the last king of France, came to an abrupt end on Feb. 24, 1848, after days of increasingly violent demonstrations in Paris and months of mounting agitation.
The protesters were fairly orderly at first. But on Feb. 23, the tide turned dark. Soldiers had fired on a crowd, gravely wounding scores of men and women. Blocks away, a journalist was "startled by the aspect of a gentleman who, without his hat, ran madly into the middle of the street, and began to harangue the passersby. 'To arms!' he cried. 'We are betrayed.' " "The effect was electric," the journalist wrote. "Far and wide the word was given that the whole system must fall."
Several decades later, in 1895, those events became grist for Gustave Le Bon's scholarly efforts to understand the mob mentality. Ever since, social scientists have sought to describe the dynamics of humans en masse. Why and how does a crowd become a mob?
The deadly assault on the U.S. Capitol on Jan. 6 has raised these questions again. If the scenes reveal one thing, it is variety. There were people in military gear, carrying guns, zip-ties and maps of the corridors; individuals in Uncle Sam hats and animal-skin costumes; others carrying nooses, planting explosive devices, breaking windows, attacking journalists; and hundreds just milling around. Many have gravitated toward using the term "mob," but the word hardly captures the totality of the events.
"Crowds do not act with one irrational mind," said James Jasper, a sociologist at the City University of New York. "There are many groups, doing different things, for different reasons. That is crucial to understanding how they ultimately behave."
Le Bon, a French intellectual, was not yet 7 during the 1848 rebellion in Paris. But he was repulsed by the entity at its center — the "howling, swarming, ragged crowd," he wrote in 1895. From there he built a theory of crowd behavior that has never quite gone away.
"The sentiments and ideas of all the persons in the gathering take one and the same direction, and their conscious personality vanishes," he said. "A collective mind is formed."
But in the middle of last century, a major shift in thinking about crowd behavior occurred, integrating two competing principles. One is that, under specific conditions, peacefully minded protesters may act out — for instance, when a barricade is broken by others, when the police strike down someone nearby.