Why does European aid to Ukraine vary? A nested analysis of domestic and international drivers

What explains variation in burden-sharing during international conflicts? We analyse the crucial case study of the full-scale Russian invasion of Ukraine since 2022 to test military burdensharing theories, exploring both domestic and international factors. Data show significant and counter-intuitive variation between countries. We employ a nested research design that combines a cross-national quantitative analysis of 35 countries' military contributions to Ukraine between 2022 and 2024 with a qualitative case study of Denmark, an unlikely case that contributes much more than predicted by theories. Our findings challenge prevailing assumptions in the burden-sharing literature by demonstrating the significant explanatory and enabling power of domestic determinants, especially public opinion, executive autonomy and government ideology. In contrast, international determinants, with the exception of strategic location, prove less influential. The case of Denmark further illustrates how overperforming burdensharing behaviour is the result of a combination of strategic incentives, such as countering the regional threat Russia poses and status-seeking behaviour, with enabling domestic conditions that allowed for high levels of aid provision. By highlighting the domestic political realities behind international contributions, this study calls for a more nuanced understanding of fair burdensharing: one that reflects both capability and willingness. The new word count is 193 and now meets the word limit.