NATO saved us and the world. No one should take it for granted — especially Donald Trump.

BERLIN — I was walking with my wife here in a cold, intermittent rain. I had just visited the Soviet War Memorial in the Tiergarten, not far from the Brandenburg Gate. We were quiet after standing before the final resting place of thousands of men who had once been our allies in the fight against the Nazis. We headed toward the Ebertstrasse, where the Berlin Wall once divided the city, and where tourists and students now milled about taking selfies in places they would have been arrested or even shot within my adult lifetime.

Perhaps it was the weather, or perhaps it was the cemetery’s grim but majestic statue of the Red Army soldier standing guard over his fallen comrades, but I found myself contemplating the chilling thought that if we had destroyed the planet in a thermonuclear war, it would likely have started not far from where my wife and I were now strolling arm in arm.

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Other wars may yet come. But we live today in an unprecedented period of peace and global cooperation, a miracle of survival we owe to the dedication and courage of a band of democracies that pledged to defend each other by signing the founding documents of the North Atlantic Treaty Organization 70 years ago in Washington.

It seems strange now to say NATO saved the world. Most people have no idea what NATO is, or why it exists. (William Crowe, former chairman of the Joint Chiefs of Staff, some years ago quipped to one of my friends that most U.S. Navy officers thought “NATO” was a Japanese admiral.) In America, President Donald Trump has tried to depict NATO as a scam or a racket, in which lazy Europeans collect American largess while doing nothing for themselves.

Republicans have rolled over on NATO

Worse, Republicans who once cheered as President Ronald Reagan stood in Berlin and challenged Soviet leader Mikhail Gorbachev to tear down the Berlin Wall now meekly nod when Trump attacks our own allies in NATO. It's a sign of how far Republicans — and Americans — have estranged themselves from one of the greatest diplomatic achievements in history.

This is not only a tragedy but also a danger, because we face a similar, if scaled-down, threat from the Russia of Vladimir Putin as we did from the old Soviet Union.

The Soviets, in their day, could not conquer and hold all of Europe. They had every intention, however, of attacking the Western outpost in divided Berlin and then drive deep into Western Europe if trouble reared its head somewhere else, such as in the Middle East or Asia. Soviet leaders assumed that at some point, the Americans and their allies would sue for peace and surrender to Moscow’s demands rather than face columns of Soviet tanks headed for Paris, Brussels and Copenhagen.

This was more than a hypothetical danger. In 1965 (in an episode unknown until after the fall of the USSR), Soviet military leaders raised the possibility of attacking West Berlin in retaliation for American moves against North Vietnam and in the Caribbean as a means of making the Americans back down and retreat to their own shores.

NATO prevented Soviet aggression

But because of NATO, an attack in Germany meant courting war not only with the United States but also with the United Kingdom, Canada, France, Portugal, Belgium, Norway, Denmark, Italy, the Netherlands and even tiny Iceland and Luxembourg, as well as countries that did not otherwise cooperate with each other, such as Greece and Turkey. The result would have been to embroil the Soviet Union in conflict with millions of people from Anchorage to Ankara, a military nightmare that would have carried the immense risk of an eventual nuclear disaster.

Today, the Kremlin regime under Putin still identifies the United States and NATO as its chief enemies. Like his predecessors, Putin is not under any illusion that he can create a new Russian empire from the southern shores of Italy to the ice fields of Norway. Rather, he is addicted to using force around Russia’s borders in order to distract his increasingly restive citizens. Like every autocrat facing his twilight years, Putin is fanning the flames of nationalism and turning the screws of military adventurism as a way of keeping himself and his cabal in power.

There is only one thing that can stand in his way: NATO.

NATO’s history is not perfect. Formed as an alliance of free nations — it did not admit Spain until 1982, well after the end of Spanish dictator Francisco Franco’s reign — it endured a near-divorce with France, a Greek detour through a military dictatorship and a storm of public opposition to modernizing NATO nuclear forces that was overcome only by the close working relationship among Reagan, British Prime Minister Margaret Thatcher and other dedicated Atlanticist leaders in Europe and Canada.

And yet in 2019, books about the Soviet Union and something once called “East Germany” gather dust in the corner of my office while NATO celebrates 70 years as the guarantor of European security.

We still need NATO to keep Russia in check

Sadly, this platinum anniversary is marred by Trump’s hostility to our most important alliance. The president does not know why NATO exists and cannot comprehend the notion of an alliance because he is unable to grasp anything that does not offer to turn a profit. But Trump’s dereliction of his duty as NATO’s leader should not prevent the rest of us from marking this milestone with respect and gratitude.

Every person who now walks through the streets of Berlin — and Toronto, and London, and Athens, and yes, even New York and Seattle and every small town in between — should reflect that they do so freely, without the shadow of either physical or political walls looming over them. They do not live in fear, as many of us once did, that every problem in the world will fall into the dark gravitational pull of a divided Europe and lead to the end of human civilization.

We should also be grateful not only that we live in freedom, but that we are alive at all. Our cities are gleaming spires and green parks, instead of piles of radioactive ash. For this, we have NATO to thank, and instead of writing yet another premature obituary to the most powerful alliance ever formed, NATO’s over half-billion citizens must find the fortitude to oppose yet another Kremlin regime that seems incapable of living at peace with its neighbors.

Previous generations accepted that challenge. So must we.

Tom Nichols is a national security professor at the Naval War College, a member of USA TODAY's Board of Contributors and author of "The Death of Expertise." The views expressed here are solely his own. Follow him on Twitter: @RadioFreeTom

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This article originally appeared on USA TODAY: NATO saved us and the world. No one should take it for granted — especially Donald Trump.