Sixth-Generation Warfare (6GW) marks the most radical rupture in the evolution of conflict: the migration of war from physical and informational domains into the cognitive and epistemic sphere. In 6GW, reality itself becomes the battlefield, as strategic focus shifts from armies and institutions to human cognition, perception, and belief. Grounded in Realism, Idealism, Hegemonic Stability Theory, and Artificial Intelligence and Cognitive Systems Theory (AICST), this chapter demonstrates how algorithmic systems now pre-empt human decision-making, manufacture consensus, and weaponise truth. Empirical case studies—including RAND AI escalation simulations, China’s Fire Eye cognitive command architecture, Sudan’s 2023 AI propaganda campaigns, and Ukraine’s cognitive front—illustrate a global shift from information manipulation to epistemic engineering. These cases reveal the emergence of “algorithmic sovereignty,” where deterrence, governance, and legitimacy are redefined by control over code and cognition. The chapter further examines the ethical and epistemic paradoxes of autonomous systems, the rise of algorithmic personhood, and the transformation of deterrence into ontological control. Concluding with a conceptual bridge towards “Peace Engineering” (Chapter 13 ) and foreshadowing quantum inflection (Chapter 8 ) as well as governance architectures (Chapter 12 ), the analysis reframes ethics as the ultimate battlefield in an era where machines not only execute war but define what war means. By integrating technological, philosophical, and ethical inquiry, this chapter positions 6GW as the ultimate synthesis of warfare’s evolution: from destroying bodies to designing minds.