During the winter of 1971-72, between 40,000 and 50,000 so-called “Iranians” were expelled from Iraq into Iran. The Iraqi government vociferously objected to any suggestion that the expulsions were motivated by anti-Shi?i sectarianism or anti-Persian racism, insisting that these “illegal immigrants” lacked proper documentation and that deportation was more “humane” than imprisonment. Breaking with past scholarship that interprets the expulsions as retribution for Iran’s take-over of the islands of Abu Musa, Greater Tunb, and Lesser Tunb, and given the relative silence about the deportations within Iraq at that time, I theorize their relationship with Iraq’s call for an aggressive policy of methodically targeting Iranians living in the Arab Gulf states for harassment, marginalization, and deportation. Coverage of the “Iranian infiltration” of the Arab Gulf countries in Al-Jumhuriyya and The Baghdad Observer newspapers and in United Nations documents related to the deportations reveals how the Iraqi government “ethnicized” a geo-strategic conflict in the Gulf to portray all Iranian nationals, and by extension Iraqi Shi?a, as a fifth column, potential participants in an expansionist plot that included Iran’s “occupation” of Arabistan/Khuzistan and its recent abrogation of the 1937 treaty establishing the border along the Shatt al-?Arab waterway. This discourse about the threat of Iranian expansionism represents a manifestation of the Iraqi Ba?th Party’s “Mesopotamianism” that intentionally framed political conflicts in the region as ethnic and sectarian conflicts played out in a pseudo-mythical frontier between Arab and Persian, Sunni and Shi?a, a forward-looking revolutionary republic against a reactionary, backwards monarchy with imperial ambitions. This project, therefore, contributes to our understanding of how the Ba?th Party categorized peoples and merged geography with history and contemporary politics as part of a broader project of regime maintenance through the formulation of a nationalist narrative of Iraq as a frontier. It shows how a particular idea of modern Iran came to represent the shu?ubi “other” to Iraq’s Arabism, and in doing so became an integral part of the Iraqi Ba?th Party’s domestic politics. Last, but not least, it provides a unique look at politics early in the 1970s, an under-studied decade of Iraqi Ba?th Party history.