This study aims to elucidate the mechanisms of transition from identity boundaries to intercultural convergence and its relationship with national cooperation for progress on Instagram, from the perspective of youth experience. The research was conducted using a qualitative method and thematic analysis. Data were collected through 24 semi-structured, face-to-face interviews with young people aged 18 to 38 living in Karaj. Purposive sampling with maximum variation was employed, and the interviews lasted between 45 and 60 minutes. The discussions were recorded and transcribed verbatim. Analysis was performed iteratively through repeated readings, semantic coding, and the organization of codes into sub-themes and main themes. To ensure qualitative validity and reliability, the criteria of credibility, dependability, confirmability, and transferability were utilized; this included peer debriefing on a portion of the coding, member checking of the thematic summaries with several participants, and the documentation of analytical decisions. The findings indicated that identity boundary-setting is primarily shaped through cultural labeling and generalizations, symbolic ridicule, lifestyle judgment, and exclusion in the comments section; it is exacerbated by the prominence of emotional content, the narrowing of social circles, brevity of messages, and communicative irresponsibility. Intercultural trust is strengthened by respect, fairness, being heard, communicative consistency, and collaborative experiences, while it is weakened by suspicion, humiliation, and the securitization of dialogue. A key result of this research is that redefining the "us" based on commonalities, restorative dialogue following tension, and issue-oriented approaches facilitate a reduction in polarization and increase readiness for collective action towards the public good. These patterns demonstrate that the fair management of interactions and the strengthening of the ethics of discourse are prerequisites for sustaining national cooperation in cyberspace.