From 1870 to 1940, racial eligibility for naturalization in the United States was limited to "free white persons" and "aliens of African nativity and persons of African descent," and many interpreted these restrictions to reflect a policy of Asian exclusion based on the conclusion that Asians were neither white nor African. Because the distinction between white and Asian was considerably unstable, however, those charged with the interpretation and implementation of the naturalization act faced difficult racial classification questions. Through archival research and a close reading of the arguments contained in the documents of the US Bureau of Naturalization, especially those documents that discussed challenges to racial eligibility for naturalization, Doug Coulson demonstrates that the strategy of foregrounding shared external threats to the nation as a means of transcending perceived racial divisions was often more important to racial classification than legal doctrine. He argues that this was due to the rapid shifts in the nation's enmities and alliances during the early twentieth century and the close relationship between race, nation, and sovereignty.