I first glimpsed the swell of hallyu, the Korean wave, a decade ago. In the winter of 2012, I was writing a story about Latina day laborers in Brooklyn who cleaned Hasidic homes before the Sabbath—when women’s work accumulated to the point where outsourcing became necessary. I had heard that many employers paid low wages or didn’t pay at all; some workers reported verbal abuse and sexual harassment. Standing among the women on a street corner in a black puffy coat, I tried to make conversation in my terrible Spanish. One morning, a worker approached me and asked, apropos of nothing, if I was Korean—not “Chinese or Japanese?” This precision was new. When I said yes, she beamed. “My daughter—she loves Korea,” she said. “She loves K-pop.”...