This thesis centres on the shift in the European Union’s strategy towards the Ukraine crisis. Its specific goal is to uncover the driving forces that caused the EU, both as a single entity and as an organisation of 27 Member States, to deviate from its historical position of preserving peace and avoiding conflicts, and become an assertive entity, utilising hard, soft and smart power to change the course of the on-going Russo-Ukrainian conflict. What is particularly interesting is the reason why the EU has decided in 2022—not 2014—to provide Ukraine with unprecedented amounts of financial, humanitarian and military aid to save a non-EU country from collapse. Considering the nature and history of the EU, the subject matter in question holds a particular interest not only for scholars or policymakers, but also for the public sphere.To help understand those driving forces, this thesis will study three theories of IR – Realism, Intergovernmentalism and Constructivism and align them with tentative explanations to explain the reasons why the EU shifted its policies towards the on-going Russo-Ukrainian conflict. Realism is going to look at how the EU has shifted away from its traditional Liberalist approach to foreign policy towards an assertive approach based on building up of power; Intergovernmentalism will dwell into the change in the inner dynamics of power within the EU, and Constructivism will examine the importance of individual leaders and their capacity to change how states behave.The ongoing Russo-Ukrainian War has transcended beyond a conflict between two nations, giving rise to a multifaceted global crisis. This crisis has manifested in severe food shortages on a global scale and has triggered a European energy crisis, resulting in excessive gas prices throughout Europe. At the same time, the on-going war in Ukraine has compelled 141 countries within the UN to collectively denounce Russia’s attack on Ukraine and has produced an unprecedented mobilisation of military aid by 45 countries throughout the world—including 24 MS of the EU—to help Ukraine defend itself from Russian dominance.The implications of the Russo-Ukrainian conflict extend to the very structure of the post-Cold War international order and its resolution holds the potential to redefine alliances between powers, reshape geopolitical boundaries and establish norms that will shape the future of IR.