The social media behemoth Facebook, which started as a social networking site for college students, has morphed into a global tech powerhouse with more than 2 billion users over the last 15 years. Lara Putnam, professor and chair of the Dietrich School's Department of History, is an expert on grassroots politics and the rise of political activism, most markedly among college-educated women. As Facebook turns 15, she also analyzes how the social media platform has transformed politics and how Americans approach activism.