The countries of NATO's eastern flank representing the so-called Bucharest Nine include Poland, Romania, Bulgaria, Estonia, Lithuania, Latvia, Slovakia, the Czech Republic, and Hungary. Over recent decades, NATO has adapted to new challenges and threats to the security environment. This article attempts to examine the ongoing armed conflict between Russia and Ukraine from the perspective of NATO's eastern flank countries as well as to answer the following research questions: are NATO member states adequately responding to the threats arising from the armed conflict between Russia and Ukraine, and will NATO be revitalised as a result of Russia's revisionist policy? The countries of NATO's eastern flank form the so-called Bucharest Nine, and include: Poland, Romania, Bulgaria, Estonia, Lithuania, Latvia, Slovakia, the Czech Republic, and Hungary (Pawłowski, 2020; Jankowski, Stępniewski, 2021). Over the decades, NATO has adapted to new challenges and threats to the security environment (Stępniewski, 2020; Stępniewski, 2011). The Alliance's need to adapt has been very clear since 2014, when Russia, with its neo-imperial policy towards Ukraine, “woke up the dragon” upon which NATO began to adapt to the new security reality in Central and Eastern Europe by increasing spending onarmaments, along with the modernisation of its armed forces, command structures, and relocation of troops, etc. Since 2014, we have been dealing with an armed confl ict between Russia and Ukraine in the Donbas (along with the annexation of Crimea by Russia), which has changed the way in which security in Eastern Europe and, more broadly, throughout Europe is perceived. As of 24 February 2022, i.e., with the start of Russia’s full-scale invasion of Ukraine, not only did the way of thinking about international order and security change, but, above all, the perception of Russia as an unpredictable participant in international relations changed also. Russia has become a serious threat and a challenge to the international order. This article attempts to look at the ongoing armed conflict between Russia and Ukraine from the perspective of NATO’s eastern flank countries as well as to answer the following research questions: are NATO member states adequately responding to the threats arising from the armed confl ict between Russia and Ukraine, and will NATO be revitalised as a result of Russia’s revisionist policy?