When President Joe Biden landed in Europe this week, it was a different continent than he had last visited in the fall of 2021.

After a month of intensive fighting in Ukraine, Russia has killed at least 1,000 civilians while an unknown number (but reportedly thousands) of Russian soldiers have died. By invading Ukraine, Russian President Vladimir Putin has catalyzed some major shifts. Germany, long averse to military spending, has decided to up its defense budget. European countries, skeptical of migrants, have welcomed Ukrainian refugees. And most of all, the North Atlantic Treaty Organization (NATO) has been revived.

Long a lethargic dinosaur of an organization, NATO this week announced new battle groups would deploy to four countries on its eastern flank, and Biden announced that the alliance would respond to Russia should it use chemical weapons in Ukraine. It’s a remarkable shift for an alliance that French President Emmanuel Macron called brain dead just two and a half years ago. And it reveals a fundamental truth of the organization: It’s an alliance meant to counter a great power adversary, for good and bad.

Biden, who has long cheered the relationship between the United States and Europe, met 29 other heads of state and the secretary general of NATO for a closed-door meeting Thursday, which Ukrainian President Volodymyr Zelenskyy joined by video. “Today’s establishment of four new battle groups in Slovakia, Romania, Bulgaria, and Hungary is a strong signal that we will collectively defend and protect every inch of NATO territory,” Biden said.

NATO summits, it might be said, are not usually very substantive. The family photo of recognizable world leaders is often the most memorable moment from these largely symbolic affairs. But NATO, an alliance forged to push back against Soviet influence in Europe during the Cold War, is designed for crisis.

Plenty of new things, in addition to the troop deployment, came out of Thursday’s meetings and in advance of them. Biden announced $1 billion in new humanitarian aid to those affected by the new refugee crisis in Europe, and a week earlier, the US had announced $1 billion more in military and security aid to Ukraine. Together with European countries, the White House and State Department announced even more sanctions on Russian politicians, military leaders, and elites, and measures to stop sanctions-evaders. Biden also said he would support throwing Russia out of the G20 club of countries with major economies.

The trip isn’t just about NATO. Biden is meeting with leaders of the European Union and the G7 countries. He will also travel to Poland, which, bordering on Ukraine, has received more than 2 million Ukrainian refugees as of this week. And Biden announced that the US will welcome 100,000 refugees from the ongoing war.

“NATO was first sort of given a new mission, or a new lease on life, by the events of 2014,” the last time Putin invaded Ukraine, said Samuel Charap, a Russia expert at the RAND Corporation. “There’s a unity of purpose now that there wasn’t before.”

How NATO is meeting the moment

The alliance of 30 countries in Europe and North America had been intended to contain the Soviet Union’s advances in the world. Yet as recently as three years ago, critics — including some world leaders — wondered if it wasn’t well suited for the geopolitics of the 21st century.

Some preeminent US foreign policy leaders argued in the 1990s that NATO wasn’t the right way for the US to engage Europe after the fall of the Soviet Union, but then as now, NATO skeptics didn’t have much sway in Washington.

Enter US President Donald Trump. Preaching a so-called America-first foreign policy, Trump often bashed NATO; he wanted allies to spend more on their militaries, and reportedly for the US to withdraw from the alliance. That stance rankled members of the Washington security establishment, but he wasn’t the only one who emphasized the alliance’s shortcomings. “What we are currently experiencing is the brain death of NATO,” Macron said in 2019.

The comment came after Trump pulled US troops out of Syria to avoid clashing with NATO ally Turkey. He withdrew those forces, however, without consulting with other NATO allies, calling into question the dependability of the Trump White House — and by extension, of the United States. US power is one of the biggest guarantors of the alliance, and Trump had battered that image.

“You have partners together in the same part of the world, and you have no coordination whatsoever of strategic decision-making between the United States and its NATO allies. None,” added Macron. He later stood by that harsh assessment.

Those criticisms, and other concerns throughout the late 2010s, led even former diplomats and scholars who were staunch supporters of the trans-Atlantic alliance to say that NATO was in crisis.

Derek Chollet and Amanda Sloat, two policy experts who are now senior Biden administration officials, wrote in Foreign Policy magazine in 2018 that NATO summits were “just not worth it” and simply too risky when Trump was in office, as he denigrated the alliance on the world stage.

Nicholas Burns, a Harvard professor who is now serving as Biden’s ambassador to China, co-wrote a paper three years ago that argued that Trump’s NATO bashing, increasingly undemocratic leaders under the NATO umbrella (among them Turkey and Hungary), and NATO’s failure to confront Putin “have hurtled the Alliance into its most worrisome crisis in memory.”

Now, NATO is a key pillar of the Biden administration’s response to the Russian invasion of Ukraine. “Putin has reinvigorated NATO in a fundamental way,” said Ivo Daalder, who served as Obama’s ambassador to NATO and now directs the Chicago Council on Global Affairs. “What Biden has done is he has reminded Americans and our allies how important NATO is.”

To deter Russia, NATO has doubled the active forces under its direct command in eastern Europe; there are now about 40,000 on the continent, in addition to the 100,000 US troops stationed there. A NATO spokesperson tweeted a graphic showing that 130 aircraft and 140 naval vessels are “on high alert.”

As NATO Secretary General Jens Stoltenberg said at the top of the summit, “NATO is providing unprecedented support to Ukraine, helping them to defend themselves.” He mentioned the “unprecedented sanctions” on Russia and NATO’s increased military presence, especially in Romania.

NATO’s stepping up to be the leader of European security. Should it?

Proponents — and there are many — of the Biden team’s response and NATO’s resurgence say this is exactly what the alliance should be doing.

NATO was the United States’ first transcontinental peacetime alliance, and maintaining it in peacetime is important, says John Manza, a former senior NATO official who is now a professor at the National Defense University. “It’s like a fire truck that’s sitting in the local fire station. You can complain and say, ‘Oh, it’s not doing anything, it’s just costing us money’ — until there’s a fire and you need it,” he told me.

NATO is learning from its last major test, in 2014, when Putin annexed Ukraine’s Crimea peninsula and later invaded the country’s eastern provinces. In response, NATO expanded its cohort of rapid response troops.

The alliance in 2018 developed a readiness plan with major land, sea, and air capabilities able to mobilize in 30 days. This month, NATO announced that it is significantly growing its forward presence to plan for potential contingencies. “Now we have enough combat power to really defend conventionally alliance territory against a near-peer competitor, like Russia,” Manza said.

Brendan Smialowski/AFP via Getty Images

The alliance, at its core, is about preventing interstate war on the European continent. “It’s absolutely what you could call NATO’s sweet spot,” said Bruce Jentleson, a Duke political scientist and fellow at the Wilson Center in Washington. “When you have sort of a superseding shared security threat, that’s when countries work together.”

That’s not to say NATO has it all figured out. “The real conundrum for NATO is the nuclear, biological, and chemical one,” said Evelyn Farkas, a senior Pentagon official for Russia, Ukraine, and Eurasia during the Obama administration. “How would they respond if there was a nuclear detonation or a nuclear weapon used by Russia? And same for chemical and biological.”

The emerging consensus among the Washington foreign policy establishment, both right and left, is that the Biden administration deserves praise for how it has handled this crisis and shepherded NATO quickly to respond to Russian aggression. NATO has been unified with providing Ukraine with weapons, sanctioning Russia, and beginning to address the new influx of refugees.

But, critics say, there are potential downsides to NATO being the only institution for European security.

Ukraine’s precarious position — with a door open to join NATO at some point in the distant future, but at the moment nowhere near meeting the conditions for the alliance’s unanimous welcome — illustrates one of the complications.

By saying, as President George W. Bush did overtly at a NATO summit in 2008, that Ukraine could and would join NATO, but not providing Ukraine with a membership action plan and a timetable to join the alliance, Ukraine has been left unprotected. It lacks the ironclad protections of the treaty’s Article 5, in which all 30 countries consider an attack on one country an attack on all of them. But at the same time, Russia internalized threats of Ukraine’s closeness to NATO.

None of this is to validate the pretexts that Putin has used to launch this war, but if NATO actually wanted Ukraine to join the alliance, maybe it should have made that happen a little more quickly. Or perhaps it should have never made the offer explicit in the first place.

Given these circumstances, critics of NATO wonder whether NATO is the best forum for ensuring European security. “The time has come for Europe to take primary responsibility for its own defense,” said Rajan Menon of the research group Defense Priorities. “It just beggars belief to me that Germany, the wealthiest country in the EU, has an army that suffers from spare parts shortages and insufficient enlisted men and women and officers.” Germany, pacifist after the Second World War, announced it would invest in its military after Putin invaded Ukraine.

It may be in Europe’s best interest to prepare its own deterrent force separately from NATO. Menon notes that, given increasing American attention toward potential conflict in Asia, Europeans should realize that the United States won’t always have the capacity to have Europe’s back. He explains that while “one can dress it up in all kinds of multilateral clothing,” NATO has always been an overwhelmingly American operation.

Beyond Europe, the United Nations could be playing a bigger role. “NATO is filling a void that the UN has created,” as Farkas put it.

What this summit means for NATO’s future

NATO has come to the fore on the issue of Ukraine. But what’s equally clear is that the transatlantic alliance is not going to be the answer to every problem of this century.

The larger question emerging from this new war in Europe is whether the US will similarly be able to mobilize global allies more broadly in the face of more existential crises of the next period. There remains a bigger global agenda that the US must take on — countering climate change, preparing for future pandemics, and strengthening the internal dynamics of democracies that are backsliding — that can’t be totally put aside by the current war.

A recalcitrant Russia and a reinvigorated NATO has major implications for the future of European security. But Jentleson, the former State Department adviser to the Obama administration, cautioned that it doesn’t change everything we think and know about the world. “Our whole foreign policy is not going to revolve around a new Cold War,” he said. “I don’t see it as defining the next era comprehensively the way that the Cold War defined the era from the late ’40s on.”

What is much more likely to define the coming decades is China as a world power, and that’s why everyone is monitoring how China navigates Russia’s war. This has practical implications. Biden administration officials have leaked that Russia has sought Chinese weapons. In Thursday’s statements from NATO heads of state, the 30 countries called on China “to abstain from supporting Russia’s war effort in any way, and to refrain from any action that helps Russia circumvent sanctions.”

The statement represented a larger acknowledgement of China as a competitor that is watching how the West responds to Russia.

In recent years, Chinese President Xi Jinping has said that the “East is rising” and the West is declining, and Putin has said that liberalism is “obsolete.” War in Europe’s east may have altered that equation and reinforced the notion that a military alliance alone is insufficient to address 21st-century problems. But some see NATO’s response — and that of non-NATO European countries alongside it — as a sign that concerted action is possible.

“The last four weeks have demonstrated that liberalism is strong and capable of standing up, and the West, if anything, is rising, not declining, if it works together,” Daalder said.