This chapter reconstructs how migration became conceptualized as a political problem within contemporary political theory. Through a critical engagement with Rawlsian liberalism, it identifies the closed system premise as a key methodological assumption that marginalizes migration. The chapter then turns to republican political theory, arguing that while the language of non-domination offers partial resources for addressing migration-related injustices, it ultimately reproduces similar constraints. By analysing both traditions, the chapter demonstrates how migration is reduced to questions of admission and integration, while emigration, temporality, and structural conditions remain under-theorized. Its main contribution lies in revealing the shared epistemological foundations that sustain the problematization of migration across otherwise divergent theoretical frameworks.