The aim of the article is to analyze the impact of the war in Ukraine on European integration. In particular, bellicist theories will be analyzed. I pose the following research questions: Has the security threat resulting from Russian imperialism prompted the European Union to develop its own defense capabilities? Did it stimulate the development of state functions of this organization, e.g. centralization or federalization aimed at guaranteeing the security of member states, especially those located in the east of the EU? I am also trying to verify the reasons why the state-building of the EU encounters difficulties in the situation of the war in Ukraine. The study was conducted during the first two years of the full-scale war in Ukraine (2022–2023).