In case anyone was in any doubt, the end of history is over. Russia’s invasion of Ukraine on Thursday 24 February finally brought down the guillotine blade on three decades of comparative international detente. Today’s Young Fabians were all born after the end of the Cold War, and we have never known armed conflict in Europe during our conscious lifetimes. Things will look very different from here.

Left-wing critics of Western foreign policy have been quick to point out that the Russian invasion is not exceptional. Alongside a range of questionable military interventions in recent years and decades, the 2003 invasion of Iraq appears most starkly similar. Then too, powerful and nuclear-armed states invaded a much weaker non-aggressor on spurious grounds, having talked up an imminent threat which never materialised - meaning that the war likely violated international law. While George Bush and Tony Blair have never answered for their actions, the argument goes, it is impossible for the West to hold Vladimir Putin to higher moral and legal standards.

These allegations are hard to dispute, especially when lined up next to other examples of Western double standards. Witness how Iran is graduating from intolerable theocracy and international pariah to worthy trading partner, just at the moment when Britain and others require an alternative source of oil imports. The intensity of moral outrage tends to very conveniently track shifting geopolitical priorities.

Nevertheless, we must all recognise the changing situation. It was easy to oppose institutions like NATO when their members were the ones destabilising the multilateral order, bombing Middle Eastern countries in an unwinnable war on ‘terror’. Matters look rather different now when you consult a map of Europe, and which states linger outside the Western security umbrella and on Putin’s doorstep. Even weeks ago it seemed inconceivable that Russia would risk a formal incursion into a territory bordering multiple NATO members. Now there are very few safe bets.

There is a convincing case that the West missed its opportunity for enduring peace. After the final dissolution of the Soviet Union in 1991, the US and its allies could have taken the proactive decision to wind up NATO altogether. That would have been the strongest gesture of goodwill for the new millennium - the recognition that a military alliance explicitly formed to guard against Stalinism had no place in a post-communist world. The nascent European Union could have acted as the continental security architecture, such as it was needed, with other institutions like the Council of Europe and the Organisation for Security and Cooperation in Europe (OSCE) including Russia in a broader multilateral framework.

Instead, the West swung the other way, expanding NATO into the old Eastern bloc and even into former republics of the Soviet Union itself. It is fully understandable that Russia perceived this as an encroachment on its sovereignty, stirring fears of encirclement which stretch back to the 1917-21 Civil War and beyond. Putin may have begun as a cautious Western ally in the struggle against Islamism, but over time the old East-West suspicion reasserted itself. Successive Western leaders could have acted sooner to avert this outcome, but ultimately it was the Kremlin that took the decision to restart war in Europe.

This is why the reaction of campaign groups like Stop the War has been so challenging for many people to swallow, including on the Left. Self-professed anti-militarists still blame NATO for provoking the present conflict, even after Russian tanks rolled over the border into Ukraine. At the most extreme, some on the far-Left are simply repeating Kremlin propaganda that the invaders are a liberation force for which the world will in the end be thankful. That argument at least has some internal consistency, but only if you are also willing to vindicate Western interventions in Afghanistan, Iraq, Libya and Syria, to name but a few this century. Imperialism is the same for the victims, whichever great power is the perpetrator.

For progressive multilateralists, this is likely to be a period of soul-searching about which option is the least-worst compromise. Young Fabians can at least reach for some precedents. The Labour Party elected in 1945 was full of people who had spent years opposing the sort of imperial power-struggles which had led to the cataclysm of the First World War. Nevertheless, this same generation recognised that conscientious objection could not overcome the threat of totalitarianism. Fresh from the military victory over fascism, Clement Attlee and Ernest Bevin managed to carry the party and the country into NATO as a defence against Stalin’s westward encroachment. Whatever NATO’s failings over the last 70 years, it has indeed acted as a cornerstone to preserve democracy in Europe.

Those are certainly not words that I ever expected to write, but they bear reflecting on in present times. Whenever Labour returns to government, it will face an utterly different international environment to the one it left in 2010, and the next generation of leaders will have to make their own choices about where Britain’s allegiances lie.

James Bartholomeusz is a Young Fabian and works in campaigns and policy at a global union federation. He writes here in a personal capacity.