In the wake of the 2010-2011 Arab Spring uprisings and the emergence of Islamist parties as leading political actors in the post-authoritarian transitions, Western analyses were teeming with predictions that not only would groups like the Muslim Brotherhood in Egypt and similar movements in other Arab countries sweep to power in their respective states, but that they would come together to form a unified front of Islamist-led governments from Morocco to Yemen. This paper seeks to interrogate the logic behind such analyses by challenging long-held assumptions regarding the relationship between Islamism and nationalism. It argues in favor of a historical approach that traces the process by which Islamist movements effectively localized what was once a universalist mission with a strong transnational component. By recasting Islamist movements as thoroughly nationalist actors operating within clearly defined political and sociocultural boundaries, we can better understand their posture in relation to domestic and regional developments. The diverging experiences of Islamist actors in the cases of Sudan and Tunisia, including their ideological formation, social mobilization, and political contestation, clearly demonstrate the impact of nationalist realities on the evolution of Islamism.