This will allow you to understand and highlight why is there so much supranationalism in the European Union? What theories can help us explain this level of integration?
Andrew Moravcsik (1993). Preferences and Power in the European Community: A Liberal Intergovernmentalist Approach. Journal of Common Market Studies 31, 473-524

Paul Pierson (1996). The Path to European Integration: A Historical Institutionalist Analysis. Comparative Political Studies 29: 123

Mark Pollack (2005). Theorizing the European Union: International Organization, Domestic Polity, or Experiment in New Governance? Annual Political Science Review8, 357-398.

Further readings:

GiadomenicoMajone (1994). The Rise of the Regulatory State in Europe. West European Politics 17 (3): 77-101

Robert D. Putnam (1988). Diplomacy and Domestic Politics: The Logic of Two-Level Games. International Organization 42:3, 427-460

Jeffrey W. Legro (1996). Culture and Preferences in the International Cooperation Two-Step. American Political Science Review 90:1, 118-137

James D. Fearon (1998). Bargaining, Enforcement, and International Cooperation. International Organization, 52:2, 269-305

Thomas Risse (2000). Let’s Argue! Communicative Action in World Politics. International Organization 54:1, 1-39

Alastair Iain Johnston (2001). Treating International Institutions as Social Environments. International Studies Quarterly 45:4, 487-515

Arthur Stein (1982). ‘Coordination and Collaboration: Regimes in an Anarchic World.’ International Organization 36:2, 299-324.

George W. Downs, David M. Rocke, et al. (1996). Is the Good News about Compliance Good News about Cooperation? International Organization 50:3, 379-406.

Andrew Moravcsik (2000). ‘The Origins of Human Rights Regimes: Democratic Delegation in Postwar Europe.’ International Organization 54:2, 217-52