The crisis in Ukraine has created a fundamentally new security situation in Europe. The transatlantic community is now faced with a revisionist power in Europe’s own backyard. Russia has shown that it is willing to use force to extend its influence and control over independent sovereign nations in blatant disregard of international law. From the onset, I have called the crisis a wake-up call. How Western democracies respond to it and reshape Euro-Atlantic security will be, I believe, the defining challenge of the next decade.

Although I am deeply concerned about a revisionist Russia, it would be a mistake to see it as the only threat. An increasingly unstable Southern neighborhood and the wider Middle East pose a range of threats to Euro-Atlantic security. Added to these, Western democracies face domestic pressures toward retrenchment and isolation, which, in turn, can diminish the will of governments to act.

The relative stability in Europe since the end of the Cold War could turn into an uncontrollable security challenge. Yet I am optimistic. Members of the North Atlantic Treaty Organization made important decisions at the alliance’s September 2014 summit in Wales to face those threats. The challenge will be to match the decisions with the resolve and resources needed in critical areas.

More Than Two Decades of Euro-Atlantic Achievements

While the crisis in Ukraine casts a long shadow, it should not obscure the historic achievements of the past twenty-five years. Europe has experienced the greatest expansion of peace, democracy, and stability in its history. Since the end of the Cold War, more than 100 million people have joined the democratic Euro-Atlantic community of nations.

This was possible because allies shared a collective vision and the will to execute it. NATO’s security guarantees and European Union integration have been two sides of this vision. Thanks to their combined efforts, countries like Poland have been able to go from dictatorships to economic powerhouses in just one generation.

During the Cold War, Europe, under the protection of the United States, was mostly a consumer of security. Over the last few decades, it has made great strides toward becoming a net provider. European members of NATO have proved their willingness to use military force by conducting dozens of operations under European Union, United Nations, and NATO banners. Along with their North American allies, they have become better at using military force as well. While in 1999 the United States conducted the vast majority of precision air strikes during the Kosovo air campaign, twelve years later it was the Europeans and Canadians that led the way during the Libya air campaign.

A stable Euro-Atlantic area was also made possible because of the efforts to associate Russia with the community. Even if cooperation was not always easy, real progress was made. This cooperation stretched from the Balkans to Afghanistan to Iran, as well as to the fight against terrorism. And significantly, the number of nuclear weapons in Europe has fallen by more than 90 percent, ending the balance of terror. Instead of mutually assured destruction, the West and Russia sought mutually assured stability.

There were setbacks. The 1990s saw the worst violence on the European continent since World War II. The bloody breakup of Yugoslavia also revealed serious shortfalls among European allies and real differences between NATO and Russia. But cooperation always prevailed, such as when Russian troops contributed to the NATO-led peacekeeping operations launched in Bosnia and Herzegovina in 1995 and in Kosovo in 1999.

At the dawn of the new century, the September 11 attacks on the United States dramatically shifted NATO’s security focus toward combating international terrorism. In solidarity with the United States, and for the first time in its history, NATO invoked Article 5—its collective defense clause that says an attack on one is an attack on all. The transatlantic community then embarked on a long and difficult fight against terrorism, often far beyond its shores.

My experiences as prime minister of Denmark and then as NATO secretary general have taught me that the path to peace and prosperity is never easy. The last two and a half decades have proved no exception. But the overall trajectory has been one of confidence in, and expansion of, the Euro-Atlantic order.

A Unique Combination of Threats

This order is now coming under increasing pressure.

A revisionist Russia means that the principles and rules that made Western-Russian relations predictable and peaceful can no longer be taken for granted. Russia’s attack on Ukraine has introduced a level of uncertainty not seen since the Cold War. Through its use of unconventional tactics—from cyberattacks and control of energy supplies to propaganda in support of its proxy forces in Ukraine—Russia has proved that it can disrupt civil society, online networks, and entire economic sectors. Its threats are all the more potent now that the country is a full part of the global economy, in stark contrast to its relative isolation during the Cold War. This growing interdependence, while I welcome it, makes NATO’s response to Russia’s disruptive tactics much more complex.

Further south, the old order in the Middle East and North Africa is breaking apart. While al-Qaeda’s core has been dealt many serious blows in recent years, regional and local jihadist groups have found new breeding grounds in the Sahel, Syria, and Iraq. Some groups, like the so-called Islamic State, are even attempting to take control of territory, posing a direct threat to the region and NATO members. These forces combine the reach of a transnational terrorist group with the means normally at the disposal of a state. Their deadly tactics are magnified by the vacuum left in the region by weak, illegitimate, or competing governments.

Added to these external risks, there is a growing internal challenge: the pressure on Western governments to retrench. Emerging from a decade of war and a major economic crisis, publics on both sides of the Atlantic are understandably tempted to turn inward. Elected governments and legislatures cannot ignore this weariness.

But the consequences are stark. With governments focused more on internal affairs, solidarity and the sharing of other allies’ concerns are more elusive. Defense has also been downgraded on the list of national priorities. Since 2008, while Russia has increased its defense spending by 50 percent, NATO members have cut theirs by 20 percent. Such cuts are not sustainable. Some allies find it increasingly difficult to conduct military operations for long periods of time. The gaps in European capabilities, such as in surveillance and reconnaissance, that existed two decades ago remain a source of weakness.

My belief is that far from being proof of a safer world, retrenchment and its consequences, like the appeasement of the 1930s, could exacerbate the risk of further war and violence.

The pressure for retrenchment is reinforced by an increasingly polarized and paralyzed international system. Today, the fractures between the permanent members of the United Nations Security Council make the prospect of launching an intervention under a United Nations mandate highly unlikely. This affects as well the need to assist countries in rebuilding their stability. I believe, for instance, that the international community’s failure to push hard enough for the establishment of a follow-on presence in Libya after the fall of Muammar Qaddafi has been a costly mistake.

I am convinced that the combination of these threats and risks, if unaddressed, could bring twenty-five years of Euro-Atlantic progress to a halt and seriously weaken the rules-based global order.

A New Sense of Confidence

The NATO summit in Wales represents the emergence of a new confidence and solidarity among allies. NATO members must now implement their decisions in full, injecting political resolve and real resources into three critical areas.

First, NATO members need a sustained increase in defense investment over the long term. Defense might be back on the agenda, but it needs to be bolstered by the necessary resources. At the Wales summit, for the first time NATO’s 28 leaders committed to reach the goal of investing 2 percent of their gross domestic products in defense within a decade. The meaning of this commitment should not be underestimated. If fulfilled, it could mark the beginning of a positive shift away from the creeping disarmament of Europe.

To have maximum effect, more spending should be matched by better spending. This means investing in critical equipment and skills as well as in research and development. Capabilities that are now in short supply, such as surveillance, reconnaissance, and strategic airlift, are critical to deal with almost all crises, whether in Europe’s East or South. At the same time, it will be crucial to maintain the ability of member states’ soldiers, military equipment, and systems to work together as one. Efforts such as Smart Defense and the Connected Forces Initiative will help nations get the most out of their defense spending and redress the important gaps that exist, particularly in Europe.

Second, allies must be willing to deal with whatever surprises they face, wherever they may come from, and be prepared to use military power when necessary. NATO does not seek conflict, but member states will come to the defense of their allies. In Wales, NATO reenergized collective defense to take greater account of the new risks Europe faces. Member states agreed to a readiness action plan to enhance their ability to respond quickly and robustly to any eventuality. The strategy includes a spearhead, quick-reaction force supported by a new strategy of reinforcement, prepositioning of equipment, and use of command and control headquarters. Together, this will mean that NATO can respond within a few days, not weeks, to any surprises. This will bring allied forces to a readiness level unseen since the Cold War.

The readiness to act must be matched in the future by the flexibility to offer a wide range of responses to complex crises. NATO members need to draw upon the lessons of recent decades to find new and smarter ways to deal with crises. In the past, the choice has too often been between large-scale military intervention and no, or too little, action.

NATO, like other international actors, must be able to act politically and to employ a wider range of tools and responses to deal with today’s complex crises. While sending troops to solve crises should never be excluded, the alliance must find other ways to project stability. This may be through providing critical support to coalitions of partners who conduct operations. Stability can also be achieved by offering more preventive measures like training and defense capacity building. At the Wales summit, NATO members decided to launch such programs in Georgia, Jordan, and Moldova to start, and possibly in Iraq later if the new Iraqi government requests the assistance.

Sharing a collective awareness and resolve to act is the third critical area. This must start with allies using NATO as a fully fledged political forum rather than just a military toolbox. There have been some significant improvements since I became secretary general in 2009. Allies now share intelligence and confer with one another like never before, including under Article 4 of NATO’s founding treaty, which calls on allies to consult each other when faced by a threat.

But I believe the West must go further. It will take a special effort from all the Euro-Atlantic institutions, not just NATO, to help Ukraine and other countries in Europe’s East transform their economies and build their own strong institutions and security. This argues for a much closer degree of coordination and unity of effort among different institutions than has been seen in recent years.

Such an effort is very much in allies’ interests. Euro-Atlantic countries cannot afford to have weak states and frozen conflicts in Europe created in part by the international community’s own failure to act. Allies should never allow a power vacuum to emerge that others can use to exert and extend their influence over the region.

NATO must also devise a new policy toward Russia: to deter and defend against any act of aggression directed at any of the allies. At the same time, if Russia is prepared to comply once again with United Nations values and Euro-Atlantic norms and principles, NATO members must remain open to dialogue and cooperation. But clearly the relationship will not be the same again unless and until Russia changes course. Russia has lost the West’s trust, and it will take a long time to regain it.

Remaining a Unique Community of Values and Resolve

The year 2014 is pivotal for the West. It is imperative that NATO members learn the lessons of the past twenty-five years and follow through on the commitments made in Wales. If allies fail, I fear for the security of the Euro-Atlantic area and for the future of the rules-based international system.

But simply returning to a Cold War mind-set would be a terrible mistake. Allies must look outward. Above all, members of the Euro-Atlantic community must summon the political will to defend their way of life using all means at their disposal, including, when necessary, the use of force. I am confident allies can and will find the resolve and the resources to ensure that the unique Euro-Atlantic community remains the anchor of the global order.

Anders Fogh Rasmussen is the secretary general of the North Atlantic Treaty Organization. Rasmussen held numerous positions in the Danish government and opposition throughout his political career, including serving as prime minister from 2001 to 2009.