Ukraine, with some western help, has won a great victory, and the original aim of Russia’s invasion – to capture Kyiv and replace the Ukrainian government – has been utterly defeated. The Russian army has now regrouped in the east for a much more limited objective: that of capturing the whole of the Russian-populated Donbas region, which Moscow has already recognised as independent. If the Russian army can achieve this in the coming weeks then we cannot say for sure what Moscow’s next move would be. However, Russia has suffered huge casualties among its elite troops, and even taking the relatively small city of Mariupol has taken two months and required reducing the city to ruins. In view of this, a further Russian campaign to capture much bigger cities such as Odesa looks implausible, and it seems possible Russia could go on the defensive, and offer a ceasefire and peace talks. Putin will pretend to the Russian people that taking a bit of extra territory in the Donbas has been a victory for Russia, but there is no need for the west to agree with him. The truth is that this war has proved a military, political and moral catastrophe for Russia. The reputation of the Russian army has been shredded; Russia’s economy is badly damaged; and the European Union is moving with surprising speed and resolution to end its dependence on Russian oil and, more slowly, gas. This would suggest that in future, Russia will be dependent on China as a market for its gas – meaning both political subordination to China and its ability to set the price for it. What are the wider implications of Russia’s defeat? The first is that on the most important issue by far – that of Ukraine’s sovereignty, independence and western alignment – Ukraine (and the west) have already won. That should allow a degree of flexibility when it comes to compromises over territorial issues, especially since most of the territories concerned have been held by Russia since 2014. Second, if there ever was a Russian plan to use Ukraine as a springboard for further aggression, that too is now over. If the Russian army cannot capture cities less than 20 miles from Russia, it is hardly likely to invade Nato. Russia will no doubt defend the positions it already holds, in defence of breakaway territories in Moldova, Georgia and Nagorno-Karabakh. If the war in Ukraine continues, there will be an increasing danger that Georgia and Azerbaijan will again seek to recover their lost territory by force. The result would be a much wider and even more dangerous conflict. Such an extension of the war will be greatly encouraged if Ukraine becomes a US proxy war against Russia, as the Biden administration apparently now intends. The defence secretary Lloyd Austin has said the US should use the war in Ukraine to “weaken” Russia in order to prevent it invading more countries. Important voices in the US and Britain have said we should help Ukraine to win a complete victory, by which they seem to mean drive Russia from all the territories it has taken since 2014, and impose such a humiliating defeat that the Putin regime is overthrown. Incredibly, it has been suggested that US support for the Mujahideen in Afghanistan in the 1980s – with all its appalling consequences for Afghanistan, the US and the Middle East – is some sort of positive model for this. Western public acceptance for the economic suffering created by sanctions has been mobilised through the argument that this is necessary to defend Ukraine and stop Russian aggression. Permanently weakening or even destroying Russia is a very different matter. Support for Ukraine is legitimate and necessary, but it has also already achieved its most important goal: that of preserving Ukrainian independence and sovereignty over the great majority of Ukrainian territory, and deterring further Russian aggression. It is also horribly dangerous. In the first place, for the Ukrainians to attack entrenched Russian positions across open country would be a very different matter from defending Ukrainian cities. The tactical advantage would inevitably shift to Russia. Ukraine could thereby suffer immense losses and turn victory into defeat. If, on the other hand, Ukraine – with western backing – did seem on the verge of complete victory, the threat to Putin’s regime and to Russian vital interests would be such that it really would seem possible Russia might escalate to missile strikes against Nato supply lines in Poland, in an effort to terrify France and Germany into making a separate peace. Once a Nato member is attacked, there will be tremendous pressure in the US to declare a no-fly zone in Ukraine – in other words, to send the US air force into action to support the Ukrainian forces on the ground. Some of these planes will then be shot down by missile batteries based in Russia itself. How long would the US accept these casualties before launching attacks on Russian territory? We would then be faced with a prospect that, during the cold war, eight US presidents took great care to avoid: Russia and Nato firing missiles into each other’s territory, and a direct conflict in Europe between two nuclear superpowers, with the ability between them to destroy humanity. US presidents did not exercise this restraint out of sympathy for the Soviet Union, but from a cold calculation of the terrible risks involved. And running these risks is unnecessary, given the strategic defeat we have already helped to inflict on Russia. Anatol Lieven is a senior fellow of the Quincy Institute for Responsible Statecraft and author of Ukraine and Russia: A Fraternal Rivalry