This paper examines South Korea’s foreign policy towards China before, during, and after the Terminal High Altitude Area Defense (THAAD) missile defense dispute to investigate the limits of South Korea’s public diplomacy and soft power. South Korea’s official public diplomacy has the objective to “gain global support for Korea’s policies,” following Joseph Nye’s narrow definition of soft power. South Korea furthermore ranks high in the most relevant soft power indices. Based on the case of Chinese economic retaliation against South Korea in response to THAAD deployment, this paper argues that public diplomacy and soft power only work in the absence of traditional security contentions, but fail in the presence of such security contentions. The THAAD case also demonstrates the utility of traditional diplomacy, based on high-level summits and negotiations, to solve the very disputes that South Korea’s latent public diplomacy and soft power were unable to alleviate.