Early analyses of the war in Ukraine emphasized several unique, case-specific factors such as the region’s complex history, Russian President Vladimir Putin’s complex psychology, and Ukrainian President Volodymyr Zelensky’s charismatic leadership. The conflict seemed shockingly new and scarily unpredictable, the end of one era and the start of another, with contours yet unknown.

As the fighting grinds on, however, the war is looking more familiar and increasingly resembles many other conflicts over the last seven decades. This suggests that general, structural features of the situation are imposing themselves on the belligerents, guiding their choices into surprisingly well-worn grooves. Ukraine, in short, is following the pattern of limited war in the nuclear age, echoing a script written in Korea and copied many times since. This is not a new era, only a new phase in the old one. And even the new phase is playing by the same old rules—with significant implications for the remainder of the war and beyond.

IT FEELS LIKE THE FIRST TIME

In the late 1940s, U.S. policymakers faced an unprecedented problem: what do you do with weapons that can destroy the world? Throughout history, states had settled their biggest differences through war. But over time, the wars had gotten more and more destructive, culminating in the total war just ended—which had itself culminated in the dropping of atomic bombs on Hiroshima and Nagasaki, destroying entire cities in a single blast. Nobody knew what would come next. Breaking the cycle of war seemed impossible. Continuing it seemed unthinkable. Tensions ratcheted up further when the Soviet Union got the bomb in 1949. And then, in June 1950, North Korean forces invaded South Korea. Washington and its allies quickly jumped in on Seoul’s side, facing off against Moscow, which along with Beijing was backing Pyongyang. How would war play out in the nuclear age? Now the question would be answered.

For three years, as brutal fighting raged up and down the Korean peninsula, the two sides gradually felt each other out and tacitly settled on rules of the road for the new epoch. Neither of the nuclear powers wanted another total war, so both put strict limits on the conflict’s means, ends, and scope. They chose not to use nuclear weapons. They chose not to attack each other’s territory or regime, keeping the fighting to the Koreas. And beyond that, the war was allowed to proceed conventionally, as viciously as the belligerents wanted.

These rules weren’t read out of a book or arrived at through negotiations. They weren’t followed out of faith, or hope, or charity. They were rooted in practicality. Policymakers in Moscow and Washington had to make crucial decisions in real time about how to pursue their objectives during the war, and the logic inherent in the situation made some courses of action much more attractive than others. Nuclear weapons, for all their power—because of all their power—turned out to be surprisingly powerless. Using them would carry many costs and bring few benefits. It would create more problems than it solved. And so neither superpower did it.

A decade later, the Cuban missile crisis reinforced the growing taboo against nuclear use and left the parties still more risk averse. Then Vietnam followed the same pattern as Korea. None of the nuclear powers, now including China, used nuclear weapons. None attacked another nuclear power’s territory or regime. And beyond that, anything went. The same rules held in the Gulf War, the Iraq War, and the Soviet and American wars in Afghanistan. They held for conflicts involving nuclear powers elsewhere (apart from some minor skirmishing). And they are holding now in Ukraine.

HOW THIS ENDS

Russia’s plan A was to conquer Ukraine quickly, install a friendly government, and present the world with a fait accompli. When that was blocked by determined military resistance, Moscow turned to plan B, pounding cities from a distance and trying to crush Ukrainian morale. When that didn’t work either, the Kremlin turned to plan C, abandoning the attempt to seize the whole country and refocusing on trying to capture and hold a swath of territory in the east and south. The coming battles in the Donbas will be crucial in shaping the outcome, but already much can be said about how this war will end.

The struggle will either conclude with a negotiated settlement involving a territorial status quo ante, or it will subside into a frozen conflict along the armies’ stalemated line of contact in the east. That is, the war’s end will resemble those in the Korean and Gulf Wars or the situation in Abkhazia, South Ossetia, and Transnistria. Either way, as in Korea, the shock of the initial aggression has galvanized a broader balancing coalition that will remain even when the fighting stops. Russia chose a hot war and will get a cold one in the bargain.

Whatever some interpretations of Russian military doctrine might suggest, Moscow will not use nuclear weapons during the conflict. Since 1945, every leader of a nuclear power, from homespun politicians such as U.S. Presidents Harry Truman and Lyndon Johnson to mass-murdering sociopaths such as Joseph Stalin and Mao Zedong, has rejected the use of nuclear weapons in battle for excellent reasons. Putin will be no exception, acting not from a soft heart but a hard head. He knows that extraordinary retaliation and universal opprobrium would follow, with no remotely comparable strategic upsides to justify them—not to mention the fact that the radioactive fallout from such use might easily blow back onto Russia itself.

For related reasons, NATO will not attack Russia or try to decapitate the Russian regime so as to avoid making Putin desperate. There will be no introduction of NATO troops, no no-fly zone, and no hot pursuit of Russian forces should they withdraw back into home territory. All these actions would carry major risks of escalation, which NATO wants to avoid as much as Moscow. Conversely, NATO will feel compelled to deny Moscow a significant victory, not just for Ukraine’s sake but to avoid setting the dangerous precedent that nuclear weapons are useful for protecting the ill-gotten gains of conventional aggression.

Within these limits, however, the war will be fought to the utmost until the tide turns decisively in one direction or curdles into a stalemate. The belligerents will struggle until they are exhausted or the battle lines return to something near the starting point. The Biden administration’s goal should be to hasten all this—by continuing to supply Ukraine with whatever conventional military aid it can short of the nuclear firebreaks, avoiding trash talk about Russian leadership, and being ready to negotiate seriously when conditions are ripe.

NUCLEAR HEDGEHOGS AND CONVENTIONAL FOXES

In the 1950s and 1960s, strategic thinkers developed elaborate speculative systems to predict how nuclear powers would behave under many different conditions. The superpowers acquired large and exquisitely baroque nuclear arsenals to signal their resolve and range up and down extensive ladders of escalation, both before and during a conflict. They considered relative disadvantages of any kind to be dangerous and poured great effort and expense into continuous modernization programs designed to keep everything up to date and convincingly scary and secure—efforts that continue today.

The lived experience of the nuclear era, however, suggests that actual political leaders in actual wars approach things more simply, seeing nuclear weapons as military hedgehogs good only for one big thing: deterrence against truly existential threats. And it suggests that such deterrence is easier than many expect. Ever since 1945, wartime leaders have not considered nuclear weapons usable, have not deployed them interchangeably with conventional weapons, and have maintained clear firebreaks to escalation. These attitudes, moreover, have held regardless of the numbers, sophistication, and structure of the nuclear forces on all sides. The balance of terror has proved to be much less delicate than originally assumed.

The one thing nuclear weapons do seem to be good for is deterring major attacks on those who have them. In this respect, the Russian invasion of Ukraine, like NATO’s 2011 campaign in Libya, will only confirm their value—not because the Russians will use them but because Ukraine didn’t have them. The war will provide yet another example of the dangers awaiting states that possess such weapons but choose to give them up. Iran and North Korea will become even less likely to accept the rollback of their own nuclear programs, reasoning that such a move could pave the way for attacks on them, too. In future arms control negotiations, therefore, Washington should dial back its ambitions and concentrate, at least for now, on trying to freeze those programs in place—a goal that, unlike rollback, might actually be achievable.

Conventional forces, meanwhile, are clearly military foxes—usable in many ways, for many objectives. It is Ukraine’s prowess in conventional combat, along with the economic and military aid it has received, that has frustrated the Russian invasion so far, and those same factors will determine how much of the east and south Kyiv is ultimately able to retain. Since future conflicts are likely to follow comparable broad patterns, U.S. defense policy should focus intensely on how to fight—and help others fight—strictly conventional wars, especially protracted defensive ones. One particular lesson stands out: the security of Taiwan will rest less on anything in the nuclear realm than on the island’s capacity to prevent an amphibious invasion from mainland China and to endure a long siege.

THE PROBLEM OF PEACEFUL CHANGE

Limited conventional wars such as the one in Ukraine are still possible in the nuclear era. General great power wars, however, are extremely unlikely. This is a great development in human history, because such wars have caused extraordinary death, destruction, and turmoil. But it is also problematic, because those same wars also served a practical function. They were the mechanism by which the international system rebalanced itself, reallocating global status and privilege to bring them into line with the underlying distribution of material power. As the political scientist Robert Gilpin noted:

The conclusion of one hegemonic war is the beginning of another cycle of growth, expansion, and eventual decline. The law of uneven growth continues to redistribute power, thus undermining the status quo established by the last hegemonic struggle. Disequilibrium replaces equilibrium, and the world moves toward a new round of hegemonic conflict. It has always been thus and always will be, until men either destroy themselves or learn to develop an effective mechanism of peaceful change.

So far, the fear of destroying themselves has led the great powers to avoid a third world war and enjoy a long peace. But history did not stop in 1945, or 1989. In recent decades, the United States has declined while China and others have risen. The frozen official arrangements for international order are increasingly unreflective of the global distribution of material power. The new cold war between Russia and the West, for example, will differ from the old one in part because major global players such as China, India, and much of the Middle East are choosing to sit this one out. Multipolarity is no longer a theory but a fact, and rising powers will increasingly demand a role in setting global rules, not just following them.

In the bad old days, such shifts in power would have led, one way or another, to a terrible general war. Because of the nuclear revolution, such wars are off the table. But since shifts in power still occur—China’s share of the global economy has quintupled over the last generation—other forms of accommodation will have to be found. It is not at all clear what that might mean in practice. But an increasingly hollow status quo cannot last forever. And absent any possibility of peaceful change, even the risk of Armageddon might not be enough to preserve it.