How do social media platforms shape individual national identities and contribute to the mobilisation for radical-right parties? It is widely accepted that digital media contributes to the spread of radical-right’s politics by selectively exposing individuals to nationalistic rhetoric, filter bubbles and misinformation. Yet, the real shift produced by digital technologies has been the transformation of citizens from passive media audiences to active media producers. This study argues that network affordances of social media enable users to engage in regressive interactions—such as hate speech, stereotyping, and trolling—with like-minded others, without fear of norm violation or sanctions. These interactions, perceived to be insulated from scrutiny, normalise and legitimise exclusionary discourse. As users gain validation, these sentiments seep into their public expressions, not only shaping the individual sense of national identity but also changing the broader discourses on national identity. Developing UNMASK, an agent-based model, the study stimulates the propagation of such discourse in online networks, and its impact on exclusionary national identity. The ABM results are validated against Twitter data on the European refugee in Germany and Italy, analysed through social network analysis and NLP techniques. The findings reveal that centralised, homophilic networks allow backstage discourse to transition into public expressions of exclusionary nationalism, whereas more decentralised, dispersed networks limit this diffusion. This paper fills a critical gap in the literature by demonstrating how the mobilisation of exclusionary nationalism unfolds at the individual level on social media networks, and how these dynamics may influence political outcomes such as voting for radical-right parties.