The research investigates the European Union (EU) andmember states’ solidarity measures in tackling global humanitarian crises. Itruns the first complete analysis of the factors that jeopardise solidarity(main objective). Such investigation results in high-impact policyrecommendations to EU institutions and member states on enhancing humanitarianaid effectiveness by bridging the gap between global humanitarian needs andinsufficient solidarity – here defined and measured as the negative deltabetween solidarity provision and actual global humanitarian needs. Accordingly,the global humanitarian financial gap is constantly increasing due to thesteady rise in the number of people in need worldwide. The EU and member statesare to increase their efforts to respond to victims of humanitarian crises(solidarity), which is the main goal of the current EU’s humanitarian strategicplan. The research thus focuses on three key EU solidarity objectives, alsocompliant with the Grand Bargain 2016: (1) coordination between EU and memberstates; (2) humanitarian-development-peace nexus and (3)humanitarianism-sustainability nexus. Implementing the nexuses requiresmultiple horizontal and vertical interactions and strong coordination betweenthe EU and member states, jointly with local implementing partners. For thefirst time, the research analyses the main challenges and identifies memberstates’ fragility as a primary obstacle to solidarity’s key objectives. Indeed,the research advances the concept of fragility as states’ (in)capacity toprovide whatever their citizens need on the economic, political, social, andcohesion dimensions. If their fragility increases (process of fragilisation),states may privilege the defence of national interest to the detriment ofsolidarity. This problem is academically still unexplored and, politically, thematter of massive efforts from the EU to bridge the gap between the increase inhumanitarian needs worldwide and the lack of sufficient financial resources.The research addresses the problem with an interdisciplinary approach. Itmainly operates in political science, international relations and Europeanstudies and integrates economics, security and development studies, andsociology. It combines academic discussion with a policy-making orientation. Itinnovatively (1) develops an interdisciplinary conceptual approach tosolidarity with the introduction of the concept of fragility; (2) tests acorrelation between fragility and solidarity by combining conceptual discussionand empirical evidence; (3) generates a new multidisciplinary analytical modeland cross-national dataset reusable in further research; and (4) providesevidence-based best practices and policy recommendations.