Both NATO and the European Community (EC), now the European Union (EU), had their origins in post-World War II efforts to bring stability to Europe. NATO's original purpose was to provide collective defense through a mutual security guarantee for the United States and its European allies to counterbalance potential threats from the Soviet Union. The European Community's purpose was to provide political stability to its members through securing democracy and free markets. Congress and successive Administrations have strongly supported both NATO and the EC/EU, based on the belief that stability in Europe has engendered the growth of democracy, reliable military allies, and strong trading partners. In the second session of the 110 th Congress, Members will likely exhibit an interest in NATO's effort to develop more mobile combat forces, enhance the alliance's role in Afghanistan, examine the appropriateness of a possible missile defense system for Europe, and enlargement of the alliance. As in the previous several years, the evolution of the NATO-EU relationship is also likely to attract congressional attention. Evolution of NATO and the EC/EU after the collapse of the Soviet Union in 1991 has brought with it some friction between the United States and several of its allies over the security responsibilities of the two organizations. These differences center around threat assessment, defense institutions, and military capabilities. European NATO allies that were also members of the EC/EU have sought from 1990 to build a security apparatus able to respond to developments believed to threaten specifically the interests of Europe. In 1990, after Iraq's invasion of Kuwait, some European governments—led by France—concluded that they lacked the military capabilities to respond beyond the North Atlantic Treaty area to distant threats. In consultation with the United States, they sought to establish the European Security and Defense Identity (ESDI) within NATO, in which they would consult among themselves and with NATO over response to a threat. Both the first Bush Administration and the Clinton Administration asked that ESDI not duplicate NATO structures, such as headquarters and a planning staff, but rather "borrow" NATO structures for planning and carrying out operations. Initial reluctance of the Clinton Administration to involve the United States in the emerging conflicts accompanying the break up of Yugoslavia led some allies to redouble their efforts to enhance their political consultation, unity, and military capabilities. They saw a threat in the form of large refugee flows, autocratic regimes, and the spread of nationalist ideas emanating from the conflict-ridden Balkans. In 1994-1996, NATO endorsed steps to build an ESDI that was "separable but not separate" from NATO to give the European allies the ability to act in crises where NATO as a whole was not engaged. In 1998-1999, the EU largely adopted ESDI as its own and began to transform it into a European Security and Defense Policy (ESDP), given greater definition by more detailed arrangements for the Europeans to borrow NATO assets for the "Petersberg tasks" (crisis management, peace operations, search and rescue, and humanitarian assistance). Britain, in a major policy reversal, joined France in moving forward discussions of these new arrangements within the EU. ESDP's principal differences with ESDI were in the effort to secure more independence from NATO tutelage and guidance in the event that the United States expressed reluctance to become involved in a crisis, a renewed discussion of more carefully outlined EU decision-making structures, and consideration of forces appropriate for potential crises. The Kosovo conflict of 1999 further spurred this effort, when most EU members of NATO conceded that they still lacked adequately mobile and sustainable forces for crisis management. All EU members express a wish to see a strong U.S.-led NATO. However, there are disputes with the United States over how or whether to involve international institutions, such as the UN, in international crises. There are also disagreements over the weight given to political versus military instruments in resolving these crises. These disputes have fueled European desires to develop a more independent ESDP. The United States maintains that ESDP must be closely tied to NATO, given the large number of states that belong to both NATO and the EU (see membership chart in Appendix ) and limited European defense resources. Congress is actively engaged in the evolving NATO-EU relationship. While Congress has supported the greater political integration that marked the European Community's evolution into the European Union, many Members have called for improved European military capabilities to share the security burden, and to ensure that NATO's post-Cold War mission embraces combating terrorism and WMD proliferation. In 1998 and again in 2003 the Senate approved the addition of new members to the alliance as a means to build European stability through securing democratic governments and adding states that shared concerns over emerging threats. During the 1998 NATO enlargement debate, Senator Jon Kyl offered an amendment to the instrument of ratification that described terrorism and the proliferation of weapons of mass destruction (WMD) as new threats that NATO must counter. The Kyl amendment called on the European allies to develop capabilities "to project power... and provide a basis for ad hoc coalitions of willing partners...." Member states should "possess national military capabilities to rapidly deploy forces over long distances, sustain operations for extended periods of time, and operate jointly with the United States in high intensity conflict." The amendment passed by a wide margin. Its essence was apparent in NATO's Strategic Concept, the alliance's strategic guidelines, adopted at the Washington summit in April 1999, and in subsequent NATO agreements to redefine the alliance's mission and to improve capabilities. The issues raised in the 1990s debate over European security remain the essence of the debate today. What are the missions in security affairs of NATO and the European Union? What is the proper weight to be given to political and military instruments in defending Europe and the United States from terrorism and proliferation? What types of military forces are necessary for NATO's role in collective defense, and for the EU's role in crisis management? Are NATO and EU decision-making structures and procedures appropriate and compatible to ensure that there is an adequate and timely response to emerging threats? What should be the role of other international institutions in responding to these threats? Issues raised by these questions are the subject of this report. There is a consensus in NATO that terrorism and the proliferation of weapons of mass destruction are the principal threats facing the allies today. NATO's 1999 Strategic Concept states that the allied "defense posture must have the capability to address appropriately and effectively the risks" associated with the proliferation of nuclear, biological, and chemical weapons. The document also describes terrorism as a threat, but indicates that political and diplomatic means should be the main instruments against both terrorism and proliferation. The attacks of September 11, 2001, on the United States led to a refinement of the allied posture on these threats. In a May 2002 communiqué, NATO agreed that the allies must "be able to field forces that can move quickly to wherever they are needed, sustain operations over distance and time, and achieve their objectives." The communiqué marks the moment that NATO decided to assume responsibilities around the globe should an ally be threatened. In November 2002, at the Prague summit, the allies made a commitment to build the capabilities necessary to go out of area. They agreed to establish a NATO Response Force (NRF) of 20,000 troops for rapid "insertion" into a theater of operations. The NRF consists of highly trained combat units from member states, and could be used to fight terrorism. In addition, the allies agreed to a scaled-down list of new capabilities, called the Prague Capabilities Commitment (PCC), that declining European defense budgets might be able to sustain. Under the PCC, some allies have agreed to develop consortia to fund jointly such systems as strategic airlift and aerial refueling, meant to provide mobility for combat operations distant from Europe, or specialized "niche" capabilities, such as special forces or units to detect chemical or biological agents. Despite the transatlantic agreement on the new common threats, the NRF, and the PCC, there are significant differences between the United States and its allies over appropriate responses. Most allied governments contend that the Administration places excessive emphasis on military over political means to counter a threat, and that the allies have other domestic budget priorities (such as pension plans) that compete with allocations for defense. The allies' response to the Bush Administration's doctrine of "pre-emptive attack" in the face of an imminent threat captures elements of the transatlantic debate over response to the threat. The Administration's National Security Strategy (2002) notes that the United States reserves the right to take military action "to forestall or prevent... hostile acts" by an adversary. While most allies would concede such a right, some view the doctrine as an example of U.S. unilateralism at the moment of U.S. global military pre-eminence. In general, they believe that military action must be undertaken within a multilateral framework. The allied debate over pre-emptive attack was affected by the U.S. decision to terminate UN weapons inspections and to go to war against Iraq in March 2003, a conflict Administration officials indicate was undertaken to prevent the Hussein regime from developing and using weapons of mass destruction against the United States and other countries. The initial refusal by France, Germany, and Belgium to approve NATO military assistance to Turkey in February 2003 in anticipation of a possible attack by Iraq sharply divided the alliance. Most allies said then, and maintain now, that a UN resolution is a requisite step, whenever possible, for NATO military action. The inability of the Bush Administration to locate WMD in Iraq led to renewed insistence among the European allies that their opposition was correct and that a UN imprimatur should be sought for NATO operations. Allied insistence on involvement of international institutions in "legitimizing" conflict has its origins in the aftermath of the 20 th century's two world wars. Europeans remain wary of arguments justifying the crossing of borders and resorting to military action.