This article examines the impact of diasporas on secessionist conflicts, focusing on the Albanian, Armenian and Chechen diasporas and the conflicts in Kosovo, Karabakh and Chechnya during the 1990s. How do diasporas radicalize these conflicts? I argue that despite differences in diaspora communal characteristics and the types of the secessionist conflicts, a common pattern of mobilization develops. Large-scale diasporic support for secessionism emerges only after independence is proclaimed by the local elites. From that point onwards diasporas become engaged in a conflict spiral, and transnational coalitions are formed between local secessionist and diaspora groups. Depending on the organizational strength of the local strategic centre and the diasporic institutions, these coalitions endure or dissipate. Diasporas exert radicalization influences on the conflict spiral on two specific junctures - when grave violations of human rights occur in the homeland and when local moderate elites start losing credibility that they can achieve the secessionist goal.