This dissertation examines the instrumentalization of radicalism during the Yugoslav wars, with a specific focus on Bosnia & Herzegovina and Croatia. Moving beyond simplistic narratives of innate ethnic hatreds, this research argues that the conflict was shaped by a synergy of internal radicalization and external power strategy. This study employs a multi-level analysis, grounded in a realist theoretical framework and utilizing Astrid Bötticher’s conceptual distinction between radicalism (reform-oriented change) and extremism (anti-pluralist violence). It posits that the elite-driven weaponization of competing Bosniak, Croatian and Serbian historical narratives provided the essential ideological catalyst for mass radicalization. This internal process was then critically enabled and intensified by the strategic interference of external powers, whose policies (including a selectively enforced arms embargo and a timed NATO intervention) furnished the military means and political coverage for extremist projects to escalate. By deliberately excluding the term “terrorism,” the analysis instead treats the systematic commission of terror as a tactical manifestation of extremism. The dissertation concludes that the wars in Bosnia & Herzegovina (1992-1995) and Croatia (1991-1995) are best understood through this nexus: where internal narratives supplied the motive (“the why”) for radicalization and external geopolitical strategy provided the capacity (“the how”), resulting in devastating conflicts whose legacy continues to define the regional landscape.