The Peace of Westphalia (1648), comprising the Treaties of Münster and Osnabrück, represents one of the most consequential diplomatic settlements in modern history. By concluding the Thirty Years' War, it institutionalized the principles of territorial sovereignty, non-intervention, and juridical equality among states (Osiander, 2001). This article examines Westphalia's enduring pillars and evaluates their resilience against twenty-first-century pressures, including economic globalization, supranational governance, non-state actors, the digital revolution, and the Responsibility to Protect (R2P) doctrine (Evans & Sahnoun, 2002). Employing doctrinal analysis, comparative historical methodology, and theoretical lenses drawn from realism, liberal institutionalism, and constructivism, the study identifies critical scholarly gaps particularly regarding cyber-sovereignty and post-colonial settings in the Global South. The article concludes that while the Westphalian framework has been tested and challenged, it persists as the bedrock of international order through adaptive evolution, and offers policy recommendations for navigating hybrid and post-territorial sovereignty challenges.