In order to embark in an orderly fashion this chapter will lay out some of the core concepts and assumptions that underpin this study. This work argues that the United States exerted significant influence on the European Union security policies during the formative years, 1998-2004. Hardly a revolutionary assertion – yet, one that is surprisingly often overlooked by EU security policy scholars. Attempts to put forward a coherent EU foreign policy have been hampered and shaped by ambiguity and inconsistency, but also by policies made in Washington, DC. This thesis is arrived at through three empirical case studies. The approach is to refine empirical findings into a more general framework in order to explain the exercise of influence in the US-EU security relationship. American theorist Jack Nagel points out three preconditions for the study of power and influence, namely to specify precisely, the time-period (i.e. from when to when?), the domain (i.e. power over whom?) and the scope (i.e. power with regard to what?).1 This work focuses on the impact of the United States on the dependent variable, namely the EU strategic culture, by focusing on key security policies during the formative years from 1998 to 2004. Less attention will be paid to the capabilities and institutions of the European Security and Defence Policy and the future of the transatlantic link, although the work is clearly also relevant to these debates.2 The criteria for the selection of the time-period and cases, that is, why certain events were chosen over others, are relatively straightforward. The 1999 Kosovo war, the 1998-2004 EU-NATO enlargements and the 2003 Iraq crisis have been chosen because they represent three momentous events in the transatlantic security partnership of the period. The disparity of these cases also helps shed light on the topic from different angles.