The sheer numbers are compelling. According to a new report from the UN security council, more than 25,000 foreign fighters are taking part in jihadi conflicts, with more and more joining in recent months. They come from more than 100 countries, meaning that half the countries in the world are providing volunteers for groups such as Islamic State and al-Qaida. If the fighting currently raging in Syria and Iraq cannot then be defined as an international, or at least internationalised conflict, it is hard to know what is.

Islamist fighters drawn from half the world's countries, says UN Read more

The international perspective includes not only the composition of the fighting groups, but the perceived risk if and when these ideologically committed and battle-hardened individuals decide to go home. The UN report notes that they pose “an immediate and long-term threat”, giving credence – if any were needed – to the long-standing fears of western intelligence services – including MI5 and MI6 – that returning fighters from Syria and Iraq could bring back with them not only a world view inimical to the country whose nationality they bear, but the military training to act in pursuit of their anti-western aims.

The report will only increase the pressure on western leaders, starting with Barack Obama, to take more aggressive measures against Isis and other jihadi groups, in the name of both national and international security. The fall of the Iraqi city of Ramadi to Isis forces earlier this month, and the Isis flag now flying above the emblematic Syrian fortress at Palmyra, together precipitated an outpouring of criticism against Obama for passivity while western civilisation burned. His US critics claimed that the US policy of air strikes, in alliance with the Gulf states and others, had been proved to be ineffective. There was now no alternative, they argued, to putting at least some American boots on the ground. Obama’s attempt at war by remote-control had failed.

Obama has continued to defend his policy of air strikes only, despite recent Isis victories

In the UK, David Cameron came in for some of the same criticism at the weekend from, among others, the former head of the army, Lord Dannatt, who claimed that air strikes alone could not do the job. He denied that he was any sort of “gung-ho” general, but called for a parliamentary debate on the dispatch of 5,000 British troops.

Almost more telling than the criticism – mainly, but not exclusively, from former military men – on both sides of the Atlantic, has been the non-response from political leaders. Obama has continued to defend his policy of air strikes only, despite recent Isis victories – most recently in an interview in Atlantic magazine, while Cameron lost no time in quashing Lord Dannatt’s suggestion via his new business secretary, Sajid Javid, who said that Syria and Iraq were not wars on the ground for British troops.

Both Obama and Cameron are right. There is no public appetite in either country for new military engagements in the wider Middle East. Past failures are too fresh in the public memory. More to the point, however, is the likely success – or otherwise – of any western military escalation. The US defence secretary, Ash Carter, said after the fall of Ramadi that Iraqi troops had shown no will to fight.

He may have been too hasty in his judgment; a counter-attack is said to be envisaged. But if the army of Iraq or the variegated rebels in Syria lack the will to win, there is no reason for western forces to support them in a fight they will be unable to sustain. Our resources are better used protecting our own security by tracking the fighters who, for whatever reason, return home.