It was in August 2014 that the real danger began, and that we heard the first warnings of war. That month, unmarked Russian troops covertly invaded eastern Ukraine, where the separatist conflict had grown out of its control. The Russian air force began harassing the neighboring Baltic states of Estonia, Latvia, and Lithuania, which are members of NATO. The US pledged that it would uphold its commitment to defend those countries as if they were American soil, and later staged military exercises a few hundred yards from Russia's border….

II. The gamble: Putin's plan to make Russia great again

Putin's answer has been to assert Russian power beyond its actual strength… wielding confusion and uncertainty — which Soviet leaders rightly avoided as existential dangers — as weapons against the West.

Unable to overtly control Eastern Europe, he has fomented risks and crises in there, sponsoring separatists in Ukraine and conducting dangerous military activity along NATO airspace and coastal borders, giving Russia more leverage there. Reasserting a Russian sphere of influence over Eastern Europe, he apparently believes, will finally give Russia security from the hostile West — and make Russia a great power once more.

Knowing his military is outmatched against the Americans, he is blurring the distinction between war and peace, deploying tactics that exist in, and thus widen, the gray between: militia violence, propaganda, cyberattacks, under a new rubric the Russian military sometimes calls "hybrid war."

Unable to cross America's red lines, Putin is doing his best to muddy them — and, to deter the Americans, muddying his own. Turning otherwise routine diplomatic and military incidents into games of high-stakes chicken favors Russia, he believes, as the West will ultimately yield to his superior will.

To solve the problem of Russia's conventional military weakness, he has dramatically lowered the threshold for when he would use nuclear weapons, hoping to terrify the West such that it will bend to avoid conflict. In public speeches, over and over, he references those weapons and his willingness to use them. He has enshrined, in Russia's official nuclear doctrine, a dangerous idea no Soviet leader ever adopted: that a nuclear war could be winnable….

Russia's aggression, born of both a desire to reengineer a European order that it views as hostile and a sense of existential weakness that justifies drastic measures, makes it far more willing to accept the dangers of war….

Today's Russia, once more the strongest nation in Europe and yet weaker than its collective enemies, calls to mind the turn-of-the-century German Empire, which Henry Kissinger described as "too big for Europe, but too small for the world." Now, as then, a rising power, propelled by nationalism, is seeking to revise the European order. Now, as then, it believes that through superior cunning, and perhaps even by proving its might, it can force a larger role for itself. Now, as then, the drift toward war is gradual and easy to miss — which is exactly what makes it so dangerous.

But unlike Ukraine, the Baltic states are all members of NATO, whose charter states that an attack on one member is an attack on them all. Whereas a Russian invasion of Ukraine prompted Western sanctions, a Russian invasion of Estonia would legally obligate the US and most of Europe to declare war on Moscow.

Less than 48 hours after Obama's address, Russian agents blanketed an Estonia-Russia border crossing with tear gas, stormed across, and kidnapped an Estonian state security officer, Eston Kohver, who specialized in counterintelligence. Kohver has been held illegally in a Russian prison for nine months now.

It was something like an act of geopolitical trolling: aggressive enough to assert Russian dominion over Estonia, but not so aggressive as to be considered a formal act of war that would trigger a Western counterattack….

The Russian military has already begun pressing the Baltic states. Russian warships were spotted in Latvian waters 40 times in 2014. Russian military flights over the Baltics are now routine, often with the planes switching off their transponders, which makes them harder to spot and increases the chances of an accident. Military activity in the region had reached Cold War levels.

Even if Russia in fact has no designs on the Baltics, its bluffing and posturing has already created the conditions for an unwanted war. In early April, for example, a Russian fighter jet crossed into the Baltic Sea and "buzzed" a US military plane, missing it by only 20 feet….

Meanwhile, Russia has been flying its nuclear-capable strategic bombers along NATO airspace, often with the planes' transponders switched off, making an accident or misperception more likely….

V. How it would happen: A plot to break NATO

Piontkovsky was trying to answer a question that Western analysts and policymakers had been puzzling over since Russian provocations began in the Baltics last fall: What does Putin want? Unlike in Ukraine, with which Russia has a long shared history, there is little demand among the Russian public for intervention in the Baltic states. They are of modest strategic value. And the risks of Russia's aggression there are potentially catastrophic. Why bother…?

Putin hopes to spark a conflict in the Baltics, Piontkovsky wrote, so as to force Western European leaders into an impossible choice: Fulfill their NATO obligation to defend the Baltics and counterattack, even if it means fighting World War III over a tiny post-Soviet republic most Europeans couldn't care less about — or do nothing….

"This is his most cherished objective," Piontkovsky told me when we talked in his kitchen, in a leafy Moscow neighborhood across the river from Gorky Park. "It's an enormous temptation. He may retreat at any stage, but the temptation is enormous, to destroy NATO. ... The risk is big, yes? But the prize is enormous."

"To destroy NATO, to demonstrate that Article V does not work, the Baltic republics of Estonia and Latvia are the best place for this," he said. "It's happening now, every day. Intrusions into the airspace, psychological pressure, the propaganda on TV…."

Then, in October, Putin warned that "open manifestations of neo-Nazism" had "become commonplace in Latvia and other Baltic states" — repeating the language that he and Russian state media had earlier used to frighten Russian speakers in Ukraine into taking up arms.

This April, several Russian outlets issued spurious reports that Latvia was planning to forcibly relocate ethnic Russians into Nazi-style ghettos — an echo of similar scaremongering Russian propaganda broadcast in the runup in Ukraine….

In early 2007, Estonia's parliament voted to relocate a Soviet-era military statue, the Bronze Soldier, that had become a cultural symbol and annual rallying point for the country's ethnic Russians. In response, Russian politicians and state media accused the Estonian government of fascism and Nazi-style discrimination against ethnic Russians; they issued false reports claiming ethnic Russians were being tortured and murdered. Protests broke out and escalated into riots and mass looting. One person was killed in the violence, and the next day hackers took many of the country's major institutions offline….

This August, as the Russian military launched its undeclared and unofficial invasion of eastern Ukraine to defend separatist rebels there against defeat, Putin attended an annual youth conference at Lake Seliger, just north of Moscow. During a Q&A session, a teaching student asked an odd question about the "cyclical" nature of history and concerns that Russia could be "drawn into a new, open global conflict."

Putin, in his answer, did something that the leaders of major nuclear powers generally avoid doing — he rattled the nuclear saber a bit:

In response, Russia has been gradually lowering its bar for when it would use nuclear weapons, and in the process upending the decades-old logic of mutually assured destruction, adding tremendous nuclear danger to any conflict in Europe ….

If an accident or miscalculation were to lead to a border skirmish, all it would take is for the Kremlin to misperceive the fighting as the beginning of an assault toward Moscow and its own doctrine would call for using nuclear weapons. Indeed, it would be the only way to avoid total defeat.

There is another layer of danger and uncertainty to this: It is not clear what Russia would consider a conventional threat worthy of a nuclear response. A few months after he'd annexed Crimea, Putin revealed that during Russia's undeclared invasion of the territory he had considered putting his country's nuclear forces on alert; his government has signaled it would consider using nuclear force to defend Crimea from an attack, something Russian analysts told me was not just bluster.

The United States, of course, has no intention of militarily retaking Crimea, despite surprisingly common fears to the contrary in Russia. But Russian paranoia about such a threat, and a possible willingness to use nuclear weapons to avert it, adds more danger to the already dangerous war in eastern Ukraine and the fears that greater Russian or Western involvement there could spark a broader conflict.

And the Crimea revelation raises a disconcerting question: Where exactly does Moscow place the line for a threat severe enough to use nuclear weapons? Its doctrine says they should be used only against an existential threat, but an attack on Crimea would be far from existentially dangerous. We can only guess where the real red line lays, and hope not to cross it by mistake.

IX. The nuclear dangers: How Putin is pushing us back to the brink

Putin has taken several steps to push Europe back toward the nuclear brink, to the logic of nuclear escalation and hair-trigger weapons that made the early 1980s, by many accounts, the most dangerous time in human history. Perhaps most drastically, he appears to have undone the 1987 INF Treaty, reintroducing the long-banned nuclear weapons.

In March, Russia announced it would place nuclear-capable bombers and medium-range, nuclear-capable Iskander missiles in the Russian enclave of Kaliningrad — only an hour, by commercial airliner, from Berlin. Meanwhile, it has been testing medium-range, land-based missiles. The missiles, to the alarm of the United States, appear to violate the INF Treaty.

This is far from Putin's only nuclear escalation. He is developing more nuclear weapons, and calling frequent attention to them, as apparent cover for his aggression and adventurism in Europe. There are suspicions, for example, that Russia may have deployed nuclear-armed submarines off of the US Eastern Seaboard.

What makes this so dangerous is that Putin appears to believe, as the scholar Edward Lucas outlined in a recent report for the Center for European Policy Analysis, that he has a greater willingness than NATO to use nuclear weapons, and thus that his superior will allows him to bully the otherwise stronger Western powers with games of nuclear chicken.

Putin is acting out of an apparent belief that increasing the nuclear threat to Europe, and as a result to his own country, is ultimately good for Russia and worth the risks. It is a gamble with the lives of hundreds of millions of Europeans, and perhaps many beyond, at stake.

X. The nuclear dangers: An atomic gun to the world's head

The view among many Western analysts is that the nuclear-capable missiles are meant as a gun against the heads of the Americans and the Europeans: You better not mess with us Russians, or who knows what we'll do.

Putin himself endorsed this view in a 2014 speech in Sochi, where he approvingly cited Soviet leader Nikita Khrushchev's 1960 address to the United Nations, when he hammered his shoe on the podium. "The United States and NATO thought, 'This Nikita is best left alone, he might just go and fire a missile. We better show some respect for them,'" Putin said….

Putin's love of brinksmanship, while perhaps born of Russia's weakness, is also deeply worrying for what it says about the leader's willingness and even eagerness to take on huge geopolitical risk.

"Either he has a very weird theory of nuclear weapons, or he just doesn’t take the West seriously and is trying to cow us with whatever threat he can make," Saideman, the political scientist, said, going on to draw yet another of the many parallels analysts have drawn to the onset of World War I.

"There are two visions of international relations: One is that threats work, and one is that threats don’t, where they cause counter-balancing," Saideman continued. "This was the theory of the [German] Kaiser before World War I: the more threatening you are, the more people will submit to your will. That might be Putin’s logic, that he’s just going to threaten and threaten and hope that NATO bends. But the long run of international relations suggests that it goes the other way, where the more threatening you are the more you produce balancing."

In other words, Putin is hoping to compensate for his weakness by expressing his willingness to go further, and to raise the stakes higher, than the more powerful Western nations. But his actions are premised on a flawed understanding of how the world works. In fact, he is virtually forcing the West to respond in kind, raising not just the risk of a possible war, but the ease with which such a war would go nuclear.

XI. The nuclear dangers: Does Putin believe nuclear war can be "won"?

That corollary is Russia's embrace of what it calls a "de-escalation" nuclear strike…. But imagine you're a Russian leader: How do you drop a nuclear bomb on NATO's troops without forcing the US to respond with a nuclear strike in kind, setting off a tit-for-tat cycle of escalation that would end in total nuclear war and global devastation?

Russia's answer, in the case of such a conflict, is to drop a single nuclear weapon — one from the family of smaller, battlefield-use nukes known as "tactical" weapons, rather than from the larger, city-destroying "strategic" nuclear weapons. The idea is that such a strike would signal Russia's willingness to use nuclear weapons, and would force the enemy to immediately end the fight rather than risk further nuclear destruction.

"Such a threat is envisioned as deterring the United States and its allies from involvement in conflicts in which Russia has an important stake, and in this sense is essentially defensive," Sokov wrote. "Yet, to be effective, such a threat also must be credible. To that end, all large-scale military exercises that Russia conducted beginning in 2000 featured simulations of limited nuclear strikes."

Seen from the Russian side, it is at least possible to imagine how this doctrine might make sense: The threat of NATO's conventional forces is widely seen as both overwhelming and imminent, making such an extreme step worth considering. Ever since the fall of the Soviet Union, Russia's strategic culture has increasingly emphasized its nuclear arsenal, the one remaining legacy of its fearsome great-power status. It is a sort of Russian cult of the nuclear weapon, or even a certain strategic fetish. With nukes so central to Russian strategic thinking, it is little wonder Moscow sees them as the solution to its greatest strategic problem.

But when you consider this doctrine from the American side, you begin to see what makes it dangerous, even insane. Imagine that you are an American leader and your forces in Eastern Europe have somehow been drawn into conflict with the Russians. Perhaps, as artillery and planes from within Russia hammer your forces, you counterattack on Russian soil to take them out. The Kremlin, fearing the start of an invasion to take Moscow, drops a tactical nuclear warhead on your forces in Estonia or Latvia. You have no idea whether more Russian nuclear strikes are coming, either on the battlefield, more widely on Europe, or even against Washington or New York. Do you respond with an in-kind tactical nuclear strike, opening the risk of gradual escalation to total nuclear war? Do you, fearing the worst, move to take out the Russian leadership before they can order more attacks? Or do you announce a unilateral ceasefire, drawing your forces back in humiliation, rewarding Russia with a victory?

Russia's nuclear doctrine is betting that any American leader — not to mention the leaders of nuclear-armed France and the UK — would choose the last of those three options. If that prediction turned out to be wrong, it would mean nuclear war, perhaps global nuclear war and thus annihilation. This doctrine, in other words, is gambling with the fate of the world….

There are yet more worrying implications to this Russian doctrine. Its logical conclusion is that Russia sees itself as able to fight a war with the conventionally superior United States without losing, and that it can do this by using battlefield nuclear weapons. Under this doctrine, Moscow is deeming not only full-blown war against the US as imaginable, but a full-blown war with at least one nuclear detonation....

"You just can't have this kind of war," Eisenhower said in 1957. "There aren't enough bulldozers to scrape the bodies off the streets."

Putin believes he has found a way around this problem, relying on smaller, battlefield-use warheads that could win a war without escalating to a global conflict in which whole cities were sacrificed.