The summer of 2016 saw one of the most significant citizen protests in the history of democratic South Korea, eventually culminating in the impeachment and conviction of then President Park Geun-hye for corruption. Concerns about the president's behavior were raised in a polarized media environment with low public trust, where extreme right-wing media outlets amplified conspiracy theories and false claims in opposition to impeachment. How then was it possible for pro-impeachment protests seeking major social change to succeed? And why did pro-Park protesters and government efforts to defend Park ultimately fail? Based on interviews with key players in the impeachment movement and original analyses of news reports and social media posts, Networked Collective Actions untangles the intricate interactions among different actors that were supported and sometimes constrained by the technological, socio-political, and legal environments in which they occurred. Moreover, Hyunjin Seo develops a theoretical framework for understanding collective actions in dynamic information ecosysems and analyzes how information consumption patterns might prompt someone to either immediately reject a certain piece of information or to reconsider and adopt that same information. Seo provides a nuanced examination of the role of journalism in a democracy where non-traditional intermediaries (e.g., social media influencers and bots) have emerged as important producers and filters of information, and in light of declining trust in news media.