In 2017–18, the Chinese Communist Party (CCP) changed its domestic security strategy in Xinjiang, escalating the use of mass detention, ideological re-education, and pressure on Uyghur diaspora networks. Commonly proposed explanations for this shift focus on domestic factors: ethnic unrest, minority policy, and regional leadership. The CCP's strategy changes in Xinjiang, however, were also likely catalyzed by changing perceptions of the threat posed by Uyghur contact with transnational Islamic militant groups in Southeast Asia and the Middle East, and a corresponding increase in perceived domestic vulnerability. This threat shifted from theoretical risk to operational reality in 2014–16, and occurred alongside a revised assessment that China's Muslim population was more vulnerable to infiltration by jihadist networks than previously believed. Belief in the need to preventively inoculate an entire population from “infection” by these networks explains the timing of the change in repressive strategy, shift toward collective detention, heavy use of re-education, and attention paid to the Uyghur diaspora. It therefore helps explain specific aspects of the timing and nature of the CCP's strategy changes in Xinjiang. These findings have implications for the study of the connections between counterterrorism and domestic repression, as well as for authoritarian preventive repression and Chinese security policy at home and abroad.