The North Atlantic Treaty Organization is the most successful defense alliance in history. Today, however, the alliance is stumbling blind, and it badly needs a new sense of common purpose. As America's next president, you will face no more important task than defining a coherent mission for NATO in the 21st century -- a mission that transcends the alliance's origins as a strictly regional pact and reinvents it as a force for global stability.

NATO was founded nearly six decades ago to protect Western Europe from a militant and expansive Soviet Union. Since the collapse of the USSR, NATO has grown and the world has shrunk. Now, in an era of growing interdependence, the vital interests of America and Europe -- and the threats to those interests -- are literally everywhere, from the melting ice of the Arctic to the killing fields of Sudan.

No longer confined to North America and Western Europe, the "free world" now encompasses liberal democracies on every continent. Asia's surging economic growth, now centered in China, has moved the world's center of gravity eastward. NATO has failed to keep pace with these changes. As an almost exclusively Western club, it is an anachronism in today's multipolar world.

You should seize the opportunity to lead NATO's transformation from a North American-European pact into a global alliance of free nations. By opening its doors to Japan, Australia, India, Chile, and a handful of other stable democracies, NATO would augment both its human and financial resources. What is more, NATO would enhance its political legitimacy to operate on a global stage.

The core purpose of this enlarged, diversified NATO would be to defend the community of open societies against terrorism, weapons of mass destruction, rogue dictators, and disorder arising from failed states. But a NATO of truly global scope also could reinforce the wider international community's efforts to keep the peace and uphold the rule of law. In situations where a broad consensus for action exists, it could work with the United Nations to stabilize conflicts, prevent genocide, and deliver humanitarian aid to victims of natural and manmade disasters.

Taking NATO global may seem like a radical leap, but in fact it is already happening. Since the Cold War ended, the alliance has improvised a series of responses to security and humanitarian crises outside NATO's traditional ambit. It has used force to stop ethnic cleansing in the Balkans; gone to war with al Qaeda and the Taliban in Afghanistan; trained police and security forces in Iraq; and delivered emergency supplies to victims of natural disasters from Indonesia to New Orleans. The question isn't whether NATO should go "out of area," it is whether NATO can do so effectively without enlisting new partners in key regions around the world.

Some will object that expanding NATO's membership in this way could divide the world into democratic and autocratic camps. You should firmly reject such fears. In the first place, the decision by democracies to band together to defend themselves did not cause the first Cold War and will not trigger a new one. Expanding NATO into Eastern and Southern Europe has brought stability to those regions, and the alliance's defensive character poses no military threat to Russia. Moreover, while membership in NATO entails adherence to liberal political values, there is no common set of authoritarian principles around which to organize an opposing coalition.

In fact, adding other leading democracies to NATO would reaffirm America's internationalist strategy, which sees our country's safety as tied ineluctably to cooperation with other free societies. It should be part of a broader strategy to update the 1940s-vintage institutions of collective security and liberal internationalism, from the United Nations to the Bretton Woods system, to reflect the new distribution of power in the 21st century.

Harry Truman put it this way in 1949, in words that still ring true: "We have learned that the defense of the United States and the defense of other freedom-loving nations are indivisible. We have learned that we can serve our country best by joining in the common defense of the rights of all mankind." A bigger, more diverse NATO could be a means of reasserting the primacy of those rights today.

NATO's Expanding Role

When the Soviet Union collapsed in 1989, the alliance had accomplished its mission. But few on either side of the Atlantic were eager to disband the West's greatest strategic asset. On the contrary, President Clinton launched the first of two waves of NATO expansion that have swelled its ranks from the original 12 members to 26. Today Albania and Croatia await entry, and, despite vehement Russian objections, Ukraine and Georgia are knocking on NATO's door.

Expansion was crucial to consolidating the allies' Cold War victory, but it did not furnish NATO with a new strategic rationale. Nonetheless, NATO has engaged in a series of ad hoc, precedent-shattering interventions. Yugoslavia's breakup posed the first post-Cold War test. In 1999, NATO reluctantly took the offensive for the first time, launching air strikes on Serbia to stop the ethnic cleansing of Muslims in Kosovo.

On the day after Sept. 11, 2001, our European partners invoked Article 5, which says that an attack on one is an attack on all. After initially (and foolishly) rebuffing our allies' offer of help in ousting the Taliban and al Qaeda from Afghanistan, President Bush relented, and NATO, in yet another first, found itself embroiled in a ground war far from its home theater of operations. In 2003, with the UN's blessing, NATO assumed command of the International Security Assistance Force (ISAF) in Afghanistan, which includes nearly 48,000 troops from 40 countries.

The Taliban's revival, however, has generated rising ISAF and civilian casualties and is feeding growing pressures in most European countries to bring troops home. Leaders in the U.S. and Europe worry, with good reason, that failure in Afghanistan would spell the end of the alliance. If NATO cannot maintain the cohesion to prevail in a conflict all agree is justified morally and strategically, how could it muster the political will to act in more ambiguous circumstances?

Persevering in Afghanistan is essential, but it will not answer the basic question hanging over the alliance: What is NATO's raison d'être in today's world of growing interdependence and multiple centers of power?

Some say that, with a newly bellicose Russia attempting to assert a "privileged sphere of influence" in Georgia and other neighboring states, NATO's original mission no longer seems so obsolete. It is certainly possible that Europe, to avoid antagonizing Russia, will slow down or postpone indefinitely Georgia and Ukraine's entry into NATO. But it is doubtful that Moscow poses a credible military threat to Europe, which today is bigger, richer, and better armed. More worrisome is the political leverage Russia gets from feeding Europe's appetite for oil and gas.

While Russia merits a watchful eye, more acute dangers facing both the United States and Europe are jihadist terrorism; Iran's drive for nuclear capabilities; Pakistan's instability; and the rise of radical groups like Hezbollah and Hamas. The allies also face common problems of global order, such as the continuing slaughter of ethnic Africans in Darfur; the outbreak of piracy around the Horn of Africa; and the growing risks of climate change.

China poses no direct security threat to the NATO partners, but its fast-growing military threatens to upset the balance of power in East Asia. Furthermore, China's stunning economic growth rates, sustained over more than two decades, have led Beijing to challenge the post-Cold War hegemony of liberal ideas by touting the superiority of its model of market Maoism.

The shifting locus of world power is the best argument for defining a new strategic mission for NATO that looks beyond Europe. In a multipolar world, neither the United States nor Europe can afford to go it alone. But even if their relative strength has eroded, transatlantic unity remains the ballast for a stable international system based on individual liberty, human rights, and the rule of law.

This alliance would be stronger still if expanded to include free nations in other, more volatile parts of the world. Likely candidates include Japan and South Korea, which have entrenched market democracy in East Asia; India, which is modernizing rapidly and dominates South Asia; Australia and New Zealand, liberal bastions in the South Pacific; and Chile and Brazil, which have stood against a rising tide of authoritarianism in South America. More controversially, some Italian leaders have even broached the idea of offering NATO membership to Israel.

NATO already is talking about developing "partnerships" with other democracies. But it ought to go a step further and develop an orderly procedure, modeled on the Partnership for Peace initiative with the former Warsaw Pact countries, for extending membership in the alliance to those that want to join.

"An active global partnership must necessarily place NATO at the center of a worldwide web of like-minded states that acts as an anchor of stability on the international system, expanding Alliance influence and integrating those willing and able to join NATO on strategic stabilization missions," says Julian Lindley-French, of the Center for Applied Policy at the University of Munich.

Offering NATO membership to some stable, non-Western democracies should be a strategic priority for the United States for several reasons:

First, it would extend NATO's military reach and resources in ways that would make Americans and citizens of other member states safer. The inclusion of such non-European powers as Japan, India, and Chile also would change the face NATO presents to the world and enhance its legitimacy in the eyes of people who traditionally have been suspicious of the West.

Second, it would bolster global stability. Just as NATO already is providing logistical support to the African Union's U.N.-sanctioned force in Darfur, an enlarged NATO would give the international community a more powerful tool for carrying out vital tasks ranging from peacekeeping to emergency relief around the world.

Third, it would continue to provide a hedge against turmoil and conflict in Eastern and Southern Europe and, if Georgia is admitted, in the Caucasus.

Fourth, it would create an incentive for rising democracies like Brazil and South Africa to stay on the path of liberal reform, lest they disqualify themselves for membership.

Costs and Risks

The idea of taking NATO global obviously must be subjected to a careful weighing of costs and benefits. Some will object that adding non-European members -- which would require a revision of the 1949 treaty -- would transplant NATO in the inhospitable soil of non-Western cultures. The same, however, could have been said about Turkey, a NATO stalwart from the beginning. Nor is it clear that the addition of, say, Japan or Australia would dilute NATO's cohesion or undermine its sense of common values and purposes more than the addition of Albania or Bulgaria.

Skeptics note that Europeans are generally more risk-averse than Americans. While the United States already offers tacit or explicit security guarantees to many of the likeliest candidates for NATO membership, Europeans might see a global NATO as a recipe for intruding the alliance into other countries' security problems, such as the family feud between North and South Korea, or the India-Pakistan standoff over Kashmir.

One of the key lessons of 9/11 is surely that ignoring conflicts in faraway countries is no guarantee of safety in today's interconnected world. Terrorists with links to al Qaeda have already struck several European capitals. A nuclear arms race in the Middle East will pose a greater danger to nearby Europe than to distant America. Turmoil in Nigeria or Central Asia could disrupt Europe's energy supplies. In addition, having cast themselves as defenders of human rights and international law, Europeans cannot in good conscience turn their faces from mass slaughter in places like Darfur or Congo.

No nation or alliance of nations can define its security any longer in narrow geographic terms. As Britain's Tony Blair has argued, political as well as economic interdependence is a fact, and a nation's self-interest increasingly depends on its ability to cooperate with other countries to solve problems it cannot solve alone. That puts an even higher premium on collective defense institutions like NATO.

On President Bush's watch, the transatlantic alliance suffered a "neardeath" experience when it split over Iraq. You must give high priority to repairing the damage and rebuilding mutual trust. More than that, however, you should offer our European partners a bold vision for refounding NATO as a global alliance capable of defending liberal ideas in a global age.

Will Marshall is president of PPI. After working on Capitol Hill and in U.S. Senate campaigns, he helped to launch the Democratic Leadership Council, where he served as policy director. He was an editor of the books With All Our Might, Mandate for Change and Building the Bridge: Ten Big Ideas to Transform America, in addition to other offerings. Marshall serves as a member of the D. C. Public Charter School Board.