In China, university students use the Internet to save the life of an attempted murder victim. In Cuba, authorities unsuccessfully try to silence an online critic by sowing seeds of distrust in her marriage. And in Russia, a lone blogger rises to become one of the most prominent opposition figures since the fall of the Soviet Union. Authoritarian governments try to isolate individuals from one another, but in the age of social media freedom of speech is impossible to contain. Online, people discover that they are not alone. As one blogger put it, "Now I know who my comrades are."
In...