Can ideas mobilize people into collective action? We investigate this question by analyzing how exposure to Communist ideology shaped an individual’s decision to join the Chinese Communist Party (CCP) during its formative stage. Our study focuses on cadets at the Whampoa Military Academy, who played crucial roles in China’s major 20th-century conflicts. Our identification strategy leverages the locality-time-content variation in the circulation of the New Youth magazine—the primary platform promoting Communism following the Treaty of Versailles in 1919—and the variation in an individual’s location over time. Comparing Whampoa cadets living in a locality with access to post-1919 New Youth against those who lived in the same locality but missed this channel, we find that the former were significantly more likely to join the CCP, and that this party choice was consequential in subsequent conflicts. We also find that family background did not predict party choice of these political pioneers, but that social networks complemented ideology exposure.
