In the wake of President Obama's recent European trip, hopes for a rejuvenation of transatlantic security cooperation continue to rise. Beyond the question of how many troops our European allies can send to fight in Afghanistan, however, renewing the alliance will require that both sides of the Atlantic come to terms with the inherent promise and practical limitations of Europe's Security and Defense Policy (ESDP). This means resolving some old problems and avoiding new pitfalls.

The justification for such a policy arose out of the Balkan wars, which suggested that after the cold war, U.S. and European interests would generally tend to coincide, but would not always be identical. The EU needed a capability to take collective action. In theory, a joint European force should be mutually beneficial: The United States benefits as Europe takes on more burdens of its own, while European states benefit from the ability to protect their interests without relying on U.S. military and political will.

Today, there is growing evidence that an independent European military policy can further common U.S. and European security interests. Since the 2003 rift over Iraq, the EU has in fact accomplished much more militarily than many observers in the United States believe. It has run successful operations in central Africa and the Balkans and carried out several smaller civilian-military missions from Europe to the Middle East to Asia.

None of these missions have been dramatic. Most are relatively short in duration. Nevertheless, they often had a discernable positive effect, either by improving the chances larger UN operations would succeed, or by taking on tasks in areas where the United States has been traditionally less interested or NATO operations are not feasible for political reasons.

The EU's main contribution to global security, however, may turn out to be less in these strictly military operations than in combined, civilian-military work. In part this is because European military capabilities will be limited by low levels of European defense spending and the fact that extensive integration of European defense budgets is unlikely. The economic slump will only make it more difficult for Europe to foot the bill for upgrades to Europe's armed forces.

But the major military interventions of the last two decades-in the Balkans, Afghanistan and Iraq-have all demonstrated the importance of civilian-military cooperation and coordination for lasting success.

And, many Europeans and Americans believe the EU has a special calling for such missions anyway, in part because of the EU's history as a "civilian" power and the practical fact that many European states have national police forces-Gendarmes, Carabinieri, etc.

The fundamental justification for an independent continental security policy-that the European Union should have the ability to respond to crises without help from the United States-remains strong, and the EU's proven track record and future civilian-military promise should encourage the United States not only to tolerate, but to actively support the development of EU military capabilities wherever possible.

Making progress will require care, however, especially when it comes to ensuring that EU-NATO relations are not poisoned by tangential disputes and unrealistic aspirations. France, Turkey, Britain and the United States will all have to work to ensure not only that ESDP succeeds, but that it develops in a direction that is beneficial to both the United States and Europe.

First and foremost, a concerted effort is needed to fix the broken working relationship between the EU and NATO, which are currently unable to enter into formal operational arrangements due to the objections of certain member states, especially Turkey and Cyprus. Turkey cites a list of grievances with the EU, but most analysts agree that the EU's refusal to offer Turkey a perspective on membership is the root of the problem.

More broadly, European states will need to continue clear and open support for NATO, lest Americans become fearful of an independent European force as a counterweight to U.S. influence. This means agreeing in practice, at least, to discuss security issues of common transatlantic concern at NATO first. It is important that a united European policy not come to be viewed as the Continental equivalent of a "coalition of the willing," operating in the face of U.S. objections.

At the same time, the United States must continue support for Europe's independent streak. This may mean a benevolent attitude toward the construction of a joint-European operational headquarters separate from NATO-even if it siphons some money from already-meager defense budgets. The United States should also be ready to support and even participate in missions with an exclusively European force when it makes sense-as it already has done by contributing police and legal officers to the EU mission in Kosovo. The trick will be figuring out where to draw the line.

The fact remains that, whatever the rhetoric, the United States and Europe will continue to share a basic interest in building a world where free societies can flourish. The EU and NATO are both, and must remain, cornerstones of any such world.

Christopher S. Chivvis is associate political scientist with the RAND Corporation in Washington, DC, an independent, nonprofit research institute. He is an expert on European security and post-conflict reconstruction and is coauthor of Europe's Role in Nation Building (RAND, 2008).