International relations theory does not offer absolute truths but provides analytical tools for understanding complex global processes. This article examines how liberalism and constructivism explain contemporary international relations through the case of the European Union. The study argues that liberalism effectively explains institutional cooperation, economic interdependence, and the role of international law, while constructivism reveals the importance of identity, norms, and shared meanings. The development of the European Union demonstrates the practical success of liberal ideas, whereas challenges such as Brexit highlight the limits of institutional integration without strong collective identity. The article concludes that combining theoretical approaches allows for a more comprehensive understanding of global politics.