Powerful states are militarizing and fortifying borders throughout the world with advanced technology. In the process, nation-states aim to assert their sovereignty by preventing irregular migration. As climate change provokes more migration, however, this dynamic challenges the hardening trajectory of nation-state territorial boundaries. I assess the impacts of this discernible trend in border construction, embodied through the term “border externalization,” as a global performance that aspires to maintain semblances of nation-state sovereignty despite transnationalizing and ungovernable forces. I cohere existing academic literature in examining to what extent the performance of nation-state sovereignty through border externalization can itself be understood as a globally-connected event via trends in intervention by powerful states, security partnerships, and integrated border technologies. I look specifically at state actions as they seek to reduce human mobility in the face of impending, irreversible, and transnationalizing climatic shifts. Combining this conclusion with literature on the impacts of borders on migrating groups, I claim that border externalization as a global event, and thereby performances of nation-state sovereignty during climate change, generate social instability.