As Russian forces gain ground in Ukraine, that country’s president and allies all seem to agree: Ukraine must fight on to victory and restore the prewar status quo. Russia would disgorge the territorial gains it has made since February. Ukraine would recognize neither the annexation of Crimea nor the secessionist statelets in the Donbas and would continue down the path toward membership in the EU and NATO.

For Russia, such an outcome would represent a clear defeat. Given the vast costs it has already paid, along with the likelihood that Western economic sanctions against it would not be lifted anytime soon, Moscow would gain less than nothing from this war. Indeed, it would be headed toward permanent enfeeblement—or in the words of US Secretary of Defense Lloyd Austin, “weakened to the degree that it can’t do the kinds of things that it has done in invading Ukraine.”

Ukraine’s backers have proposed two pathways to victory. The first leads through Ukraine. With help from the West, the argument runs, Ukraine can defeat Russia on the battlefield, either depleting its forces through attrition or shrewdly outmaneuvering it. The second path runs through Moscow. With some combination of battlefield gains and economic pressure, the West can convince Russian President Vladimir Putin to end the war—or convince someone in his circle to forcibly replace him.

But both theories of victory rest on shaky foundations. In Ukraine, the Russian army is likely strong enough to defend most of its gains. In Russia, the economy is autonomous enough and Putin’s grip tight enough that the president cannot be coerced into giving up those gains, either. The most likely outcome of the current strategy, then, is not a Ukrainian triumph but a long, bloody, and ultimately indecisive war. A drawn-out conflict would be costly not only in terms of the loss of human life and economic damage but also in terms of escalation—including the potential use of nuclear weapons.

Ukraine’s leaders and its backers speak as if victory is just around the corner. But that view increasingly appears to be a fantasy. Ukraine and the West should therefore reconsider their ambitions and shift from a strategy of winning the war toward a more realistic approach: finding a diplomatic compromise that ends the fighting.

Victory on the battlefield?

Many in the West contend that the war can be won on the ground. In this scenario, Ukraine would destroy the Russian army’s combat power, causing Russian forces to retreat or collapse. Early on during the war, boosters of Ukraine argued that Russia could be defeated through attrition. Simple math seemed to tell the story of a Russian army on the verge of collapse. In April, the British defense ministry estimated that 15,000 Russian soldiers had died in Ukraine. Assuming that the number of wounded was three times as high, which was the average experience during World War II, that would imply that roughly 60,000 Russians had been knocked out of commission. Initial Western estimates put the size of the frontline Russian force in Ukraine at 120 battalion tactical groups, which would total at most 120,000 people. If these casualty estimates were correct, the strength of most Russian combat units would have fallen below 50 percent, a figure that experts suggest renders a combat unit at least temporarily ineffective.

These early estimates now look overly optimistic. If they were accurate, the Russian army ought to have collapsed by now. Instead, it has managed slow but steady gains in the Donbas. Although it is possible that the attrition theory could one day prove correct, that seems unlikely. The Russians appear to have suffered fewer losses than many thought or have nonetheless found a way to keep many of their units up to fighting strength. One way or another, they are finding reserves, despite their stated unwillingness to send recent conscripts or mobilized reservists to the front. And if push came to shove, they could abandon that reluctance.

If the collapse-through-attrition theory seems to have failed the test of battle already, there is another option: the Ukrainians could outmaneuver the Russians. Ukraine’s forces could beat the enemy in mechanized warfare, with tanks and accompanying infantry and artillery, just as Israel beat its Arab enemies in the 1967 Six-Day War and the 1973 Yom Kippur War. Neither Russia nor Ukraine has sufficient mechanized combat units to densely defend their vast fronts, which means in principle that either side should be vulnerable to rapid, hard-hitting mechanized attacks. So far, however, neither side appears to have resorted to such tactics. Russia may be finding that it cannot concentrate forces for such attacks without being observed by Western intelligence, and Ukraine may suffer from similar scrutiny by Russian intelligence. That said, a cagey defender such as Ukraine could lure its enemy into overextending itself. Russian forces could find their flanks and supply lines vulnerable to counterattacks—as appears to have occurred on a small scale around Kyiv in the early battles of the war.

But just as the Russian army is unlikely to collapse through attrition, it is also unlikely to lose by being outmaneuvered. The Russians now seem wise to the gambits Ukraine tried early on. And although details are scarce, Ukraine’s recent counterattacks in the Kherson region do not appear to involve much surprise or maneuver. Rather, they seem to look like the kind of slow, grinding offensives that the Russians have themselves mounted in the Donbas. It is unlikely that this pattern will change much. Although the Ukrainians, because they are defending their homeland, are more motivated than the Russians, there is no reason to believe that they are inherently superior at mechanized warfare. Excellence at that requires a great deal of planning and training. Yes, the Ukrainians have profited from Western advising, but the West itself may be out of practice with such operations, having not waged mechanized warfare since 2003, when the United States invaded Iraq. And since 2014, the Ukrainians have focused their efforts on preparing forces for the defense of fortified lines in the Donbas, not for mobile warfare.

More important, a country’s ability to conduct mechanized warfare correlates with its socioeconomic development. Both technical and managerial skills are needed to keep thousands of machines and electronic devices in working order and to coordinate far-flung, fast-moving combat units in real time. Ukraine and Russia have similarly skilled populations from which to draw their soldiers, so it is unlikely that the former enjoys an advantage in mechanized warfare.

A possible counterargument is that the West could supply Ukraine with such superior technology that it could best the Russians, helping Kyiv defeat its enemy through either attrition or mobile warfare. But this theory is also fanciful. Russia enjoys a three-to-one advantage in population and economic output, a gap that even the highest-tech tools would be hard-pressed to close. Advanced Western weapons, such as the Javelin and NLAW antitank guided missiles, have probably helped Ukraine exact a high price from the Russians. But so far, this technology has largely been used to leverage the tactical advantages that defenders already enjoy—cover, concealment, and the ability to channel enemy forces through natural and manmade obstacles. It is much harder to exploit advanced technology to go on the offense against an adversary that possesses a significant quantitative advantage, because doing so requires overcoming both superior numbers and the tactical advantages of defense. In the case of Ukraine, it is not obvious what special technology the West possesses that would so advantage the Ukrainian military that it could crack Russian defenses.

To comprehend the difficulty Ukraine faces, consider Nazi Germany’s failure in its last major offensive of World War II, the Battle of the Bulge. In December 1944, the Germans surprised the Allies in the Ardennes Forest with a concentration of mechanized and infantry divisions against a thinly defended 50-mile stretch of front. They hoped to shatter the Allied defenses in Belgium, split the US and British Armies, take the critical port of Antwerp, and stall the Allied war effort. The Wehrmacht bet that its skill at armored warfare, its laboriously assembled local numerical superiority, and its advanced armored vehicle technology would overcome the combined advantages that the US and British militaries enjoyed in terms of manpower, artillery, and airpower. Although the Germans were able to achieve surprise and enjoyed a few days of success, the operation soon foundered. Western commanders quickly figured out what was going on and efficiently used their materiel superiority to beat back the advance. Today, some seem to be suggesting that the Ukrainians try a strategy similar to the Germans to overcome similar constraints. But there is no compelling reason to believe that the Ukrainians would fare any better.

Winning in Moscow?

If Kyiv can’t win on the battlefield in Ukraine, perhaps it can achieve a victory in Moscow. This, the other main theory of victory, imagines that a combination of battlefield attrition and economic pressure could elicit a decision on Russia’s part to end the war and relinquish its gains.

In this theory, battlefield attrition mobilizes the family members of slain, injured, and suffering Russian soldiers against Putin, while economic pressure makes the lives of average Russians ever more dismal. Putin watches his popularity wane and begins to fear that his political career could soon end if he doesn’t stop the war. Alternatively, Putin doesn’t see how fast battlefield attrition and economic privation are undercutting his support, but others in his circle do, and in their own naked self-interest, they depose and perhaps even execute him. Once in power, they sue for peace. Either way, Russia concedes defeat.

But this path to Ukrainian victory is also strewn with obstacles. For one thing, Putin is a veteran intelligence professional who presumably knows a lot about conspiracies, including how to defend against them. This alone makes a strategy of regime change suspect, even if there were some in Moscow who were willing to risk their lives to try it. For another thing, squeezing the Russian economy is unlikely to produce sufficient privation to create meaningful political pressure against Putin. The West can make the lives of Russians a bit drabber, and it can deprive Russian weapons manufacturers of sophisticated imported electronic subcomponents. But these achievements seem unlikely to shake Putin or his rule. Russia is a vast and populous country, with ample arable land, plentiful energy supplies, lots of other natural resources, and a big, if dated, industrial base. US President Donald Trump tried and failed to strangle Iran, a much smaller and less developed but equally energy independent country. It is hard to see how the same strategy will work against Russia.

The effect of casualties on Putin’s calculations of his own interests is harder to assess. Again, however, there is reason to be skeptical that this factor will convince him to retreat. Great powers often incur major war losses for years, even for flimsy reasons. The United States did so in Vietnam, Afghanistan, and Iraq; the Soviet Union did so in Afghanistan. Before Russia’s invasion in February, many in the West insisted that the Ukrainians organize for a guerrilla insurgency against Russia. The hope was that this prospect would deter a Russian attack in the first place or, failing that, exact such a high price from Russian forces that they would soon depart. One problem with this strategy is that insurgents themselves must suffer a lot for the privilege of imposing a high price on their occupiers. Ukrainians may be willing to incur painful losses in a conventional war of attrition against Russia, but it is not clear that they can inflict enough pain to achieve the victory they want.

Nor is it clear that they can sustain such losses for a long time. Even the most patriotic soldiers can run out of patience if the fighting seems futile. If mounting casualties require Ukraine to throw ever less prepared troops into a hopeless battle, support for an open-ended war of attrition would erode even further. At the same time, the Russians are likely to have a high tolerance for pain. Putin has so controlled the domestic narrative about his war that many Russian citizens see the fight the same way he does—as a crucial battle for national security. And Russia has more people than Ukraine.

To the negotiating table

Nobody can say with certainty that the Russian army cannot be hit hard enough or cleverly enough to induce its collapse or that Russia cannot be hurt enough to induce Putin to surrender. But these outcomes are highly improbable. At present, the most plausible result after months or years of fighting is a stalemate close to the current battle lines. Ukraine should be able to stop Russian advances, thanks to its highly motivated force, infusions of Western support, and the tactical advantages of the defense. Yet Russia enjoys superior troop numbers, and that, plus the tactical advantages of defense, should allow it to thwart Ukrainian counterattacks designed to reverse its gains. In Russia, Western sanctions will annoy the population and set back economic development, but the country’s self-sufficient supply of energy and raw materials should prevent the measures from achieving anything more than that. In the West, meanwhile, populations inconvenienced by the collateral damage of sanctions could themselves lose patience with the war. Western support of Ukraine may become less generous. Taken together, these factors point to one outcome: a draw on the battlefield.

As the months and years go on, Russia and Ukraine will both have suffered a lot to achieve not very much more than what each has already achieved—limited and pyrrhic territorial gains for Russia, and a strong, independent, and sovereign government with control over most of its prewar territory for Ukraine. At some point, then, the two countries will likely find it expedient to negotiate. Both sides will have to recognize that these must be true negotiations, in which each must give up something of value.

If that is the most likely eventual outcome, then it makes little sense for Western countries to funnel even more weapons and money into a war that results in more death and destruction with every passing week. Ukraine’s allies should continue to provide the resources that the country needs to defend itself from further Russian attacks, but they should not encourage it to expend resources on counteroffensives that will likely prove futile. Rather, the West should move toward the negotiating table now.

To be sure, diplomacy would be an experiment with uncertain results. But so is the continued combat necessary to test Ukrainian and Western theories of victory. The difference between the two experiments is that diplomacy is cheap. Besides time, airfare, and coffee, its only costs are political. For example, participants may leak details of negotiations for the purpose of discrediting one camp or another, destroying a particular proposal and generating political opprobrium. Such political costs pale in comparison to costs of continued war, however.

And those costs could easily grow. The war in Ukraine could escalate to include even more destructive attacks by either side. Russian and NATO units operate in proximity at sea and in the air, and accidents are possible. Other states, such as Belarus and Moldova, could get drawn into the war, with knock-on risks for neighboring NATO countries. Even more frightening, Russia possesses powerful and diverse nuclear forces, and the imminent collapse of its effort in Ukraine might tempt Putin to use them.

A negotiated solution to the war would no doubt be hard to achieve, but the outlines of a settlement are already visible. Each side would have to make painful concessions. Ukraine would have to relinquish considerable territory and do so in writing. Russia would need to relinquish some of its battlefield gains and renounce future territorial claims. To prevent a future Russian attack, Ukraine would surely need strong assurances of U.S. and European military support, as well as continuing military aid (but consisting mainly of defensive, not offensive, weapons). Russia would need to acknowledge the legitimacy of such arrangements. The West would need to agree to relax many of the economic sanctions it has placed on Russia. NATO and Russia would need to launch a new set of negotiations to limit the intensity of military deployments and interactions along their respective frontiers. US leadership would be essential to a diplomatic solution. Because the United States is Ukraine’s principal backer and the organizer of the West’s economic pressure campaign against Russia, it possesses the greatest leverage over the two parties.

It is easier to state these principles than it is to hammer them into the implementable provisions of an agreement. But that is precisely why negotiations should start sooner rather than later. The Ukrainian and Western theories of victory have been built on weak reasoning. At best, they are a costly avenue to a painful stalemate that leaves much Ukrainian territory in Russian hands. If this is the best that can be hoped for after additional months or years of fighting, then there is only one responsible thing to do: seek a diplomatic end to the war now.

Barry R Posen is Ford International Professor of Political Science at MIT.