After a four-year break, K-pop supergroup BTS returned on Saturday with a massive and free comeback concert in Seoul, where thousands of police locked down a central boulevard for the Netflix-exclusive spectacle that drew tens of thousands of fans. All seven members of the band – RM, Jin, Suga, J-Hope, Jimin, V and Jung Kook – recently completed South Korea’s mandatory military service and hope to reclaim their status as one of the world’s biggest pop acts. Organisers of the concert, which...