China has banned all overseas performers that "threaten national sovereignty" following a performance by Bjork in Shanghai earlier this year. At that concert, the Icelandic singer led the crowd in a chant of "Tibet, Tibet!" after performing her song "Declare Independence." The ban will also fall on artists who "threaten national unity", "whip up ethnic hatred", "violate religious policy or cultural norms" or "advocate obscenity or feudalism and superstition." Plus, all performances must be approved beforehand, right down to what encores will be played. The move was made as China's Ministry of Culture gears up for this year's Olympic Games, which is expected to attract protesters and unruly crowds that don't need to be exacerbated by musicians.