Remarkably, that was all it took to spark conflict. Before they even met, the boys began to call members of the other group “outsiders” and “intruders.” Merely being part of one group and aware of another was enough to create hostility.

Later research has found that “symbolic” threats, like perceived differences in values or beliefs, will arouse even greater enmity between groups. Studies have shown, for instance, that people are more likely to be antagonistic to immigrants if they perceive them as threatening the country’s values than if they view them as direct competition for jobs or other resources.

‘It’s Like a Depression’

The National Front’s politics take advantage of these natural human tendencies. But the party also has tapped into a sense of social dislocation, even despair, because of changes brought by globalization and technological progress. This phenomenon, too, can be seen in Fréjus.

Walk a few minutes from the cathedral and you will arrive in a small shop that offers manicures and a colorful selection of beauty products. Behind the counter, I met Helene Beaumurs, an elegantly coifed brunette whose glowing complexion was a testament to her wares. She grew quiet when I asked about the National Front’s rise here.

She was not sure whether she would support Ms. Le Pen, she said. But she had lost faith so completely in France’s mainstream politicians that anything — even a party long considered taboo — seemed like an improvement.

Today she sees a way of life she cherishes eroding. She knows farmers who are struggling, working seven days a week but barely getting by. In the center of town, stores are closing as they struggle to compete with large supermarkets, she said, gesturing at the vacant storefronts on the narrow, winding street.

“I think there are many people in France who want to know why they get up in the morning, and if working still has the value they were taught as children,” she said, “or if it’s just pulling the cart.”