As Europe teeters on the brink of a dangerous era of instability, the Germans are debating a possible withdrawal from NATO’s nuclear sharing arrangements, the British and French are squabbling over fish, and the EU is chastising the Poles, Lithuanians — even the Ukrainians — for how they are going about defending their territorial sovereignty against hostile forces.

Either Europe has failed to grasp the gravity of the moment or, if aware, lacks the strategic foresight, courage, and diplomatic will to act accordingly. Both are daunting prospects. Should Europe flounder, it could soon find its security environment permanently altered.

The threats that Europe faces are many and varied. Internal divisions, a revisionist and globally assertive China, and — most alarmingly for the region — an emboldened Kremlin, all tug at the ostensible ideal of European cohesion.

Russia’s strongman Vladimir Putin holds to a different ideal, at the center of which lies a grandly restored ‘Great Russia.’ He has weaponized thousands of migrants and, with Minsk as his sidekick, has been forcing them towards Belarus’ border with Poland, Lithuania, and Latvia. Russian nuclear bombers have been flown down the North Sea and into the English Channel; anti-satellite missiles have been tested.

A winter energy shortage spurred by cut Russian gas supplies menaces much of Central and Eastern Europe. On Ukraine’s northern and eastern borders, 100,000 troops of Russia’s most elite military units stand at the ready.

The immediate aim is to prevent Ukraine from crossing the Kremlin’s red line and joining NATO. The wider objective is to fold Ukraine into greater Russia. Of this Mr. Putin makes no secret. He openly denies Ukrainian independence and insists on Kiev’s centrality to Russian statehood. Ukraine is today sovereign, claims Mr. Putin, because “Russia was robbed.”

How far Mr. Putin will go to rectify this alleged theft is to be seen. Ukraine’s military is today stronger than when the Kremlin seized Crimea in 2014. In the event of an incursion, it is capable of a formidable challenge. Yet with EU member states unlikely to provide Ukraine with additional assistance, any challenge by its forces could prove an insufficient deterrent against Mr. Putin’s aggression.

Murmurs of a Russian offensive in 2022 suggest the Kremlin may have assessed the risk of conflict to be more appealing than that of the status quo. The surrender of Ukraine to Russia would be disastrous for Europe and the West. Much like Catherine the Great, Mr. Putin claims he cannot defend Russian frontiers without expanding them. Ukraine could then be but the first of his territorial demands.

Additional exigencies accompanying Mr. Putin’s saber-rattling are likewise gloomy echoes or Europe’s not-so-distant past: the removal of U.S. tactical missile defense from Europe, lifting sanctions placed on his regime, ostensibly terminating the Dayton Agreement, and granting him the unfettered ability to gallivant the globe in pursuit of his revisionist interests.

Could the entire Cold War settlement be at risk of unraveling?

Intelligence estimates often fail because of the apparent impossibility of reconciling facts with analysis. This was the story behind Russia’s 2008 Georgian invasion. Despite mounting evidence, it was difficult to imagine that Moscow would act. With history as a cruel teacher, Europe’s seeming lack of urgency is as curious as it is concerning. Despite the EU’s calls of “concern” and threats of “grave consequences,” the overall sentiment is one of appeasement.

The reality is that Europe remains largely disarmed and distracted, behaving as though not much has changed in the global power distribution since the 1990s. The unwillingness of key European powers to properly resource their defense has created a security imbalance in the region, which is now compounded by the ruminations over nuclear missiles.

Even if Germany’s new government decides to remain in NATO’s nuclear arrangements, its long–term commitment will remain an open question. With such a jumble, how can Europe reasonably parry an ostensible Russian offensive?

Speaking before the EU Commission in September, the EU president, Ursula von der Leyen, called for greater European “political will” on defense, and the establishment of a European Defense Union. What such a union might entail and what it will do is unclear. What is clear is that the Europeans need to get their act together — before it’s too late.