Challenges Facing the Tax System in Wartime and Directions for Its Reform Taking into account European Trends

The article is devoted to analyzing the key challenges facing Ukraine's tax system in the context of full-scale war, assessing their impact on fiscal stability, and justifying directions for its reform, taking into account current European trends, best international practices, and the provisions of the National Revenue Strategy until 2030. It has been proven that wartime and post-war economic, social, and security shocks significantly increase the requirements for adaptability, transparency, and sustainability of tax policy, and therefore require systemic changes in approaches to its formation and implementation. It is argued that the effective transformation of the tax system should combine harmonization with European standards, taking into account Ukrainian wartime and post-war realities, ensuring a balance between fiscal sustainability, economic development, and social justice. It has been established that some of the most important areas of reform are: harmonization of indirect taxation rules and reduction of losses from non-payment of value added tax and excise tax; modernization of corporate taxation and prevention of profit shifting abroad through the implementation of anti-BEPS measures and a global minimum tax; improving personal income taxation, taking into account social justice and targeted benefits; developing property taxation with a transition to market-based approaches to property valuation; introducing investment incentives with clear deadlines and performance criteria; applying mechanisms for temporary taxation of excess profits during periods of price and energy crises; accelerating the digitization of tax administration through the integration of information systems, automation of control, and real-time data exchange. A conceptual model for reforming Ukraine's tax system has been proposed, combining adaptation to EU best practices, minimization of tax risks, and ensuring resilience to military and post-war challenges. It is argued that the implementation of the outlined measures will contribute to the formation of a stable, transparent, and effective tax system capable of ensuring predictable budget revenues, supporting economic recovery, increasing the competitiveness of the economy, strengthening taxpayer confidence, and integrating Ukraine into a single European tax space. The results obtained form the theoretical and methodological basis for further research into tax policy instruments, mechanisms for monitoring their effectiveness, and strategies for adapting the Ukrainian tax system to EU standards.