Purpose: This study explores the impact of NATO's eastward expansion on regional security, particularly its consequences for Russia and the broader international system. It examines NATO’s response to the Russo-Ukrainian conflict and evaluates how this response has affected the unity of the alliance and the effectiveness of conflict management mechanisms.

Research Methodology: This study uses a qualitative approach based on secondary sources, such as journal articles, government publications, and international news. It employs content analysis to assess NATO policies, Russia's strategic reactions, and the evolving security dynamics in Eastern Europe. The theoretical framework applied is collective security, which focuses on NATO’s collective defense obligations and their influence on relations with Russia.

Results: NATO's response has strengthened solidarity but caused internal divisions due to national interests. NATO’s expansion has worsened relations with Russia, leading to military interventions. Conventional conflict resolution methods, especially the UN Security Council (UNSC), have been ineffective, shifting the focus to alternative diplomatic platforms.

Conclusions: NATO’s expansion has intensified tensions with Russia, challenging existing conflict resolution mechanisms. This study suggests that NATO engage in dialogue with Russia and reassess its enlargement policy to address modern security issues effectively.

Limitations: This study relies on secondary data sources, which may limit the scope of the analysis and exclude firsthand perspectives from key decision-makers. Additionally, it does not assess the direct impacts of NATO actions on countries outside of the immediate Russia-NATO relationship.

Contributions: This research provides insights for international relations and security studies, helping policymakers, scholars, and international organizations navigate NATO’s role in global security and conflict resolution.