Over the last few years, the idea of “the one percent” has become a popular way to discuss the gap between the fantastically wealthy—the one percent of Americans who control more than 20 percent of the country’s wealth—and the rest of us. But the one percent is not a new phenomenon. Back in 1900, they were known as the Robber Barons—people like Andrew Carnegie and Philip Armour, who were riding new industries and monopolies to ever greater fortunes. At the …