This thesis addresses a critical puzzle in the study of American political violence: why do such a wide array of actors – from white supremacists and militia groups to disaffected veterans and suburban conservatives – participate in right-wing anti-government extremism? While much of the existing literature focuses on ideological or economic explanations, this study advances a structural argument rooted in war-driven radicalisation. It argues that divisive U.S. foreign conflicts – those which betray initial public expectations of being quick, justified, and low-cost – create a fertile environment for domestic extremist mobilisation. Through a comparative case study of World War I, the Vietnam War, and the post-9/11 Wars on Terror, the thesis traces how public disillusionment with these conflicts eroded trust in government, normalised political violence, and enabled the growth of radical movements. These wars did not merely produce fringe anger but catalysed broader shifts in political identity, creating a spectrum of alienation that pulled individuals from across the ideological centre toward extremism. By isolating the causal mechanisms linking foreign conflict to domestic unrest, this research offers a novel framework for understanding how war can reshape the internal political landscape, highlighting the unintended, long-term consequences of U.S. foreign policy on democratic stability at home.