In 1956, Moscow sent tanks and troops into Hungary, killing thousands of protesters as it crushed an anti-Communist uprising. Twelve years later the Soviet Union attacked Czechoslovakia, putting a brutal end to the “Prague Spring” and its liberal reforms. In 1991, Soviet tanks and armored personnel carriers assaulted crowds of civilians defending the independence of Lithuania. Russia fomented a war against Georgia in 2008, illegally seizing the territories of Abkhazia and South Ossetia. Most murderous of all has been Russia’s savage onslaught against Ukraine, which began in 2014 with the conquest of Crimea and exploded in February 2022 into a full-scale invasion aimed at overthrowing the pro-Western government of Volodymyr Zelensky.

All the countries attacked by Russia in the years since World War II have this in common: None was a member of NATO at the time of Moscow’s aggression. By contrast, no nation sheltered under the Atlantic Alliance umbrella has ever been menaced by Russian violence.

The enlargement of NATO from 12 members in 1949 to 31 members today is one of the most successful achievements of modern diplomacy. Former secretary of state Madeleine Albright was right when she predicted in 1997 that making the alliance bigger would “expand the area of Europe where wars do not happen.” Unfortunately, NATO didn’t expand enough. In 2008, Ukraine was assured that it would be admitted — eventually — but the allies were never in a hurry to make good on that assurance. Right-wing isolationists, left-wing appeasers, elite pundits, and so-called realists all warned that extending NATO to Russia’s borders would provoke Vladimir Putin to launch a war. Ukraine was left hanging, its fate unresolved.

And the result? Keeping Ukraine out of NATO didn’t assuage Russian hostility. It inflamed it. The allies let themselves be persuaded that if they declined to admit Ukraine, Putin would not resort to bloodshed. In reality, they made bloodshed more likely. The horrific slaughter and destruction of the last 16 months would never have happened had Ukraine’s accession not been endlessly postponed.

It’s time that changed.

When the leaders of NATO’s member states convene for their annual summit in Vilnius, Lithuania, on Tuesday, admitting Ukraine as a member should be the first item on the agenda. Whatever objections there may have been in the past to welcoming Ukraine as a full-fledged ally, this war ought to have dispelled them.

Ukraine is now indispensable to the defense of the West and the European security order laid down after World War II. No nation is paying a higher price to oppose the Kremlin’s barbarism and rapacity — or paying it with greater courage and grit. Ukrainians have been battling for considerably more than just the security of their own national borders. “They are representing all of our values, European values, and they are fighting for all of us,” said Sanna Marin, who stepped down last month as Finland’s prime minister. Ukraine is literally on the front line between Russia and the free democracies of Europe. For NATO to keep holding Ukrainians at arm’s length, after everything they have done for the West, would be a moral disgrace.

It would also be a serious military blunder.

When it comes to the essential purpose for which NATO was created — deterring, confronting, and defeating Russia in battle — Ukraine today has more experience than any other nation. “Ukraine is now fighting the kind of war for which NATO has so long prepared,” Newsweek’s diplomatic correspondent David Brennan wrote in April. “The country is flooded with NATO weaponry, with which Ukrainian troops are inflicting enormous losses on the Russian invaders.”

The government in Kyiv has built up its military to NATO standards, sharing what it learns with members of the alliance. Ukrainians by the hundreds of thousands have honed their ability to fight a modern, high-intensity war against Europe’s deadliest aggressor and most brazen war criminal. That makes Ukraine an unparalleled asset, one the alliance can no longer afford to deny itself.

The naysayers who balked at bringing Ukraine into the alliance for fear of unleashing Putin’s rage turned out to be grievously wrong. Now the naysayers insist that there can be no Ukrainian accession while the war is ongoing. They fear that under NATO’s Article 5 — under which an armed attack on any member of the alliance “shall be considered an attack against them all” — the entire alliance might be pulled into the war with Moscow. Given the risk of a third world war, with both sides in possession of nuclear weapons, leaders like German Foreign Minister Annalena Baerbock flatly insist that NATO “cannot talk about accepting new members in the midst of a war.”

But the naysayers are wrong again. NATO’s collective defense clause does not mean that admitting Ukraine in wartime would oblige every NATO ally to dispatch troops to the battlefield, let alone to deploy nukes. The language of Article 5 is clear. It requires only that each member take “such action as it deems necessary” to aid an ally under attack. That may, but need not, include the use of armed force.

For nearly a year and a half, the United States and its European allies have rallied impressively behind Ukraine’s government. They have showered Kyiv with economic and humanitarian aid. They have sustained its war effort with arms, ammunition, and gear. They have provided lockstep diplomatic support for Ukraine in international forums. They have enforced harsh sanctions against Russia. At this point, Ukraine’s membership should be considered a fait accompli. Formalizing Ukraine’s status as a NATO ally would not trigger World War III, but it would confront Putin with the final proof that his bid to destroy Ukraine’s independence and separate it from the West has failed.

As former Ukrainian defense minister Andriy Zagorodnyuk points out, “with its massive support for Ukraine during the past 15 months, the alliance has in essence already paid all the costs of admitting Ukraine.” NATO ought to begin reaping the benefits of that investment. Confirming Ukraine as a permanent NATO ally would undermine Putin’s resolve to keep fighting. That in turn would expand the zone of safety and security defended by the alliance — the part of Europe “where wars do not happen.”

Ukraine has received a great deal from NATO — military supplies, intelligence, training, and technology. But it asks no other country to put boots on the ground. “It has no reason to,” Zagorodnyuk writes. “Unlike smaller NATO states, Ukraine has a vast military force that can handle the Russians all by itself.”

The sooner Ukraine joins the alliance, the sooner Putin’s war will end. The Ukrainians have proved their loyalty to the West as few potential allies ever have. It is time now to permanently reciprocate that loyalty and bring Ukraine, once and for all, into NATO’s fold.