Chinese Foreign Minister Qin Gang was removed after a mystery disappearance, then systematically erased from ministry websites in a sign the one-time Xi Jinping favorite was purged. Like his monthlong absence, Qin’s replacement by foreign policy chief Wang Yi went unexplained, with ministry spokespersons dodging questions about Qin and former colleagues staying mum online. History suggests the world might never get an explanation from Beijing on why it has purged Qin.