Justified and enforced: Explaining the legitimization and execution of mass deportation of undocumented migrants

In the 21st century, between 2000 and 2025, an estimated 8–9 million people were deported en masse globally. Mass deportation remains a major recurring issue in international relations. The number of deportees in the last five years, from 2020 to 2025, is more than in the first 20 years of the 21st century, from 2000 to 2020. This thesis examines how states justify, legitimize, and execute mass deportation, and investigates what these actions reveal about the current state of migrants' rights. By distinguishing deportation from other forms of removal, this study provides necessary conceptual clarity. I argue that to justify mass deportation, states increasingly employ securitization rhetoric, often coupled with a 'fifth column' narrative. Because not all states resort to mass deportation, I have developed a new three-level analytical framework to examine the legitimization and execution of these cases at domestic, regional, and international levels; each level has two elements: laws and actors. This framework is applied to two paired-comparison case studies where justifications for mass deportation were present, yet the outcomes differed. Furthermore, the impact of mass deportation on migrants' rights is evaluated through a rigorous analysis of international laws and conventions. This thesis fills a significant gap in the literature by providing conceptual clarity and a new analytical framework. By analyzing two of the most recent cases as of 2025, the study helps clarify how states justify, legitimize, and execute the mass deportation of migrants and concludes with policy recommendations aimed at addressing systemic shortcomings and protecting the rights of migrants, particularly undocumented migrants.