--- - |2 This article examines the changing geopolitical realities which have redefined the nature of sovereign governance on the Sino‐Vietnamese border. The binary forms of classification in a rigidly and clearly delimited Sino‐Vietnamese borderland replace the ambiguous space of “zomia,” with its fluid and overlapping identifications. This dynamic context sets the conditions for local communities and their long‐standing tradition of ethnic marriages straddling the borders of China and its neighboring states. In order to understand how, and why, the status of previously accepted forms of undocumented ethnic marriage has recently changed from “common” (shishi) to “illegal” (feifa) in two ethnic Yao villages, I look at various factors. These include how state discourses on marriage migration in Asia, biopolitical concerns about population security in China, and regional iterations of the global anti‐human trafficking campaign, come into play in forceful ways to shape the geopolitical regime of the Sino‐Vietnamese borderland and redefine the terms of legitimate practices, thus reconfiguring ethnic marriages as illegal. - 'International Political Sociology, Volume 9, Issue 4, Page 352-368, December 2015. '