Why did the European Union face obstacles from nationalism and national sovereignty?

The European Union (EU) has frequently encountered obstacles from nationalism and national sovereignty because the nation-state remains the primary focus of political loyalty for most people. While the EU represents a significant effort toward supranational integration, its most ambitious goals—which require limiting national authority—often clash with the enduring belief that supreme loyalty should be directed toward the sovereign state.1

Key factors contributing to these obstacles include:

• Sovereignty Concerns: Many citizens and political leaders fear that EU integration infringes upon their country's sovereignty. For example, during the ratification of the Maastricht Treaty, voters in Denmark initially rejected the agreement due to concerns over such infringements.2
• Policy Conflicts: The EU’s move toward common policies often conflicts with established national practices. The elimination of border controls, for instance, necessitated new Europe-wide policies that challenged existing national immigration, asylum, and residency frameworks.2
• Economic and Political Control: The transition to a common currency required member states to relinquish control over their own monetary policy and adhere to strict fiscal criteria, a significant surrender of traditional national power.2

Ultimately, nationalism acts as a persistent barrier to deeper unification, as states remain protective of their freedom of action and their ability to determine domestic policy.1