When protests erupted across the United States late last year, after grand juries failed to indict the police officers who killed Michael Brown and Eric Garner, a friend who works for a prominent media outlet wrote to me wondering “if it’s all just the internet organizing itself.” The nationwide marches and freeway blockades seemed spontaneous, after all, with the Twitter hashtag #BlackLivesMatter being widely used to publicize gathering spots and share images of the demonstrations.