The European Union’s military involvement in the Western Balkans, particularly through European Union Force (EUFOR) Althea in Bosnia and Herzegovina, is grounded in a multilayered legal framework that draws on EU treaties, international law, and regional peace agreements. Established under the Common Security and Defence Policy (CSDP) and authorized by UN Security Council Resolution 1575 (2004), Althea represents a rare example of EU-led military deployment with a UN mandate. It is the largest mission launched by the European Union to this day. While the mission plays an important role in supporting public security and implementing the Dayton Peace Agreement, it also reveals the EU’s limited legal and institutional capacity to address structural issues like constitutional dysfunction, ethno-nationalism, and secessionist threats. The reliance on soft power and minimal military presence reflects the EU’s constrained ability to enforce durable peace, while the continued necessity of EUFOR underscores both the fragility of the region’s stability and the limitations of existing legal instruments in securing long-term constitutional cohesion.