A 16-year-old boy has been sentenced to three and a half years in prison by a Hong Kong court for joining a Taiwan-based political group that promoted the city’s independence, in breach of the national security law. The boy, who earlier pleaded guilty to conspiracy to commit secession, was found on Monday to be an “active participant” in the activities of the Hong Kong Democratic Independence Union, in which he served as secretary. The Union, founded by fugitive Alan Keung Ka-wai, advocated Hong...