To do those officials credit, they saw that serial mendacity was only a short-term solution to their problems and the news about China’s calamitous defeats could not be permanently suppressed. But they believed that by the time this became apparent, one of their country’s hidden strengths would have kicked in which would give them a tremendous advantage in any drawn-out conflict.

China’s secret war winner – officials had been told by their expert advisers – was that China was the world’s leading producer of rhubarb. This was much used in traditional Chinese medicine and was deemed the only effective cure for constipation. These experts confidently advised the policy-makers of the day that all they needed to do was to cut off the West from its rhubarb supplies and its leaders would ultimately be forced to grovel for peace.

Of course, it is easy enough to deride the ludicrous wishful thinking of those long forgotten mandarins, explaining away defeat and vainly seeking to stem the barbarian advance. But their self-delusions have much in common with those of Western and Middle Eastern politicians, soldiers and diplomats seeking to halt the seemingly unstoppable progress of Islamic State (Isis) in Iraq and Syria in the 12 months since Isis captured Mosul on 10 June 2014.

Grim experience had not prevented Western and regional leaders from being influenced by gusts of false optimism. Before the fall of Mosul, nobody seemed to pay much attention to the fact that Isis had captured Fallujah and was operating freely from the Iranian border to Aleppo. After Isis seized much of northern and western Iraq last June, one might have expected it to be taken seriously, and so it was, briefly. But then Middle East conspiracy theorists intervened, claiming that Isis was just the old Baath party disguised in Islamic garb, while in Baghdad it became conventional wisdom that Isis had done a deal with the Kurds who had stabbed the Iraqi army in the back.

This widely believed theory of an Isis-Kurdish plot was knocked on the head when Isis attacked and defeated the Iraqi Kurds in August. But Isis action provoked a US air campaign against Isis, and American air strikes were central to stopping Isis from overrunning the Syrian Kurdish militia fighting heroically to hold the city of Kobani during a four-and-a-half month siege.

Earlier this year, the Pentagon produced a fantastical scenario about an imminent recapture of Tikrit, and on 31 March Iraqi government finally took over the small city after a month-long assault. At around about this time I noticed that I was treated with scepticism when I tried to persuade people that Isis was getting stronger rather than weaker. True, Isis had failed to take Kobani, but it had stood up to a pounding by at least 700 US airstrikes in a confined area, strong proof of its forces’ discipline and resolution. I spoke to many leaving Isis and they confirmed that Isis was conscripting local young men everywhere. If the self-declared caliphate has a population of six million, then its recruitment pool is very large.

Isis did not fight hard for Tikrit and may have held it with as few as 500 fighters. Yet its fall led to absurdly exaggerated hopes in Baghdad and worldwide that Isis was collapsing, though there was little real evidence for this. More important, the Iraqi army was not coming back together after the defeats of last year. One Iraqi security official estimated to me that its real strike force was only between 10,000 and 12,000 men (Golden Division, Swat and a few other units). This was before the Ramadi débâcle.

The real military balance of power between Isis and its enemies – so different from self-deceiving propaganda – was made all too apparent on 17 May when Isis defeated elite Iraqi soldiers to take Ramadi. Four days later, on 21 May in Syria, Isis routed the Syrian army and captured Palmyra and has since struck at Syrian opposition units north of Aleppo and at the north-eastern city of Hasaka.

Three points need to be made about why these victories are particularly significant. Firstly, Isis is attacking on multiple fronts many hundreds of kilometres apart, showing greater military strength than last year. Secondly, it is winning despite US airstrikes that were supposed to have stopped it in its tracks and to be grinding it down. Thirdly, these latest attacks did not come as a surprise as at Mosul, but, even though they had been foreseen, the Iraqi and Syrian armies were unable to stop them.

How did Western policy-makers react to these stunning defeats? Sadly, their response was very similar to those Chinese officials a couple of centuries back. They denied the extent of the military disasters and pretended that it is Isis which is on the retreat. The US Deputy Secretary of State Antony Blinken claimed that the territory Isis controls is getting smaller and “more than 10,000” Isis fighters have been killed in US airstrikes. The first point is probably untrue and is, in any case, meaningless in a quasi-guerrilla war, while high Isis casualties suggest it has far more men under arms than is generally believed if it is still attacking in so many places at the same time. The UK Foreign Secretary Philip Hammond was insisting that the capture of Tikrit, for which Isis did not fight hard, was more important than the fall of Ramadi for which the Iraqi army had battled for months. Both men were speaking in the wake of a conference in Paris which was about how to combat extremists and which had decided that no new strategy was necessary.

Many of the leaders at this meeting were evidently hearing soothing words from their advisers and intelligence services about how some contemporary version of the Chinese rhubarb monopoly will doom Isis to long-term defeat. Over the past year I have listened to a torrent of spurious reasons why Isis will ultimately be defeated, though none of them have been borne out by events. A US favourite used to be “arming the Sunni tribes”, but this only just worked in 2006-07, when backed by 150,000 US troops, and in Iraq against al-Qaeda, which was much weaker than Isis. Tribes in Iraq and Syria that tried this a second time round have been slaughtered.

Optimists reassure me that Isis will wither away because its extremism and violence are disliked by the people it rules. This may be true of its sentiments, but it has no plans to run for election and will kill anybody who opposes it. Others argue that Isis is running out of money, which, even if correct, is not going put out of business a religious cult of great savagery that believes it is divinely inspired. Isis can be defeated but only when total priority is given to doing so and when policy-makers reject self-deceiving recipes for bringing about its demise.

By Patrick Cockburn