A hundred years ago, a character who was to enter the bloodstream of 20th-century popular culture made his first appearance in the world of literature. In his day he became as well known as Count Dracula or Sherlock Holmes: he was the evil genius called Dr. Fu Manchu, described at the beginning of the first story in which he appeared as "the yellow peril incarnate in one man." Why did the idea that the Chinese were a threat to Western civilization...