After thirteen years, the west is giving the appearance of winding down its military presence in Afghanistan. Britain's combat-operations ended on 26 October 2014, while Nato's are due to finish by 31 December. Behind the scenes, however, a less overt effort is underway to ensure a continued presence.

The United States military, for example, will still deploy up to 10,000 individuals in Afghanistan, most likely including many special forces and others supporting drone-operations. There will in addition be many thousands of people employed by private-security companies. In both cases the precise roles are often less than clear.

The British military's involvement will be channelled through the new Resolute Support training-mission, which will have around 500 UK personnel. Here too there are surrogate groups whose function is unknown, though hundreds of Gurkhas, perhaps up to 1,000, will it seems help protect British diplomats and other civilians.

The UK is also increasing the numbers of troops deployed to train, mentor and assist Iraqi army soldiers. The ministry of defence insists they are trainers rather than combat-troops. This is no doubt true in a strict sense in that they will not go out on offensive patrols; but individuals are well nigh certain to be armed and to have dedicated close protection. At present the contingent may number in the low hundreds, but could be increased.

The leading western powers are thus repositioning their military involvement in the main theatres of the "war on terror". It is useful to see what is happening on the other side in similar terms. For adaptation is also the key to understanding the Islamic State, and the wider movement it is part of - with the added element that this movement has a long-term outlook shaped both by ideology and generations of combat experience.

The context

The starting-point here is opposition to the Soviet occupation of Afghanistan in the early and mid-1980s. The mujahideen were strongly supported by the Pakistani Inter-Service Intelligence (ISI) and the CIA but by the middle of the decade substantial numbers of the mujahideen were motivated by religious belief in addition to, and even instead of, more nationalist motives. This was even more the case with the foreign fighters travelling from across the Middle East and beyond to join the struggle for an Islamic state against the perfidious Soviet occupiers.

By 1989 the Soviets had been defeated and were gone. Osama bin Laden, Ayman al-Zawahiri and the combat-trained al-Qaida cohorts dispersed; many went to Saudi Arabia, then to Sudan and then finally back to Afghanistan, where they supported the Islamist Taliban as it sought to defeat the Northern Alliance warlords. Many of the Taliban themselves had fought against the Soviets. By the end of the 1990s, with the civil war almost won, there was a solid generation of combat-trained Islamists in Afghanistan, many with worldwide connections.

After 9/11 most of the al-Qaida elements survived and scattered once more. In 2003 a new war erupted with the western occupation of Iraq, once again attracting young men from across the region and beyond. The 2004-08 period, in particular, gave rise to yet another generation of hardened Islamist paramilitaries. This time, though, there were two important differences.

First, many of these fighters had substantial combat experience but also technical competence in such areas as improvised explosive devices, and the other was that they were fighting highly trained and very well-equipped western military in urban environments, a very different and much tougher environment than the fight against Soviet conscripts in rural Afghanistan two decades earlier.

Second, in Iraq large numbers of paramilitaries ended up engaging the best trained and equipped elite US and UK forces of Task Force 145 - SAS troopers, Rangers, SEAL-Team 6 and Delta Force - in the bitter shadow war that peaked with Operation Arcadia in 2006. Many thousands of them were killed or detained. The latter spent years in huge prisons like Camp Bucca near Basra, which at times contained 20,000 detainees; one of those held was Abu Bakr al-Baghdadi, the “Caliph” of Islamic State.

At the heart of IS is a cohort of highly experienced and determined men, mainly Iraqis, who come from that background and represent a new generation of Islamist paramilitaries with clear links to their predecessors. The cycle of paramilitary connectivity stretches over more three decades from the early 1980s to (so far) the mid-2010s.

The struggle

In this light, Islamic State can be seen as part of a wider trend which preceded it and will long outlast this particular movement. The eschatological dimension of the original al-Qaida idea - which goes way beyond an earthly life that might think in terms of mere decades - means that the current wave is, in the view of ideologues, just one phase in an enduring struggle.

The phase began with the campaign in Afghanistan against the Soviets in the 1980s, then the tussle with the Northern Alliance in the 1990s, then against two huge western coalitions in Iraq and Afghanistan after 9/11. Now, thirty years later, the main effort is against the west once more, in Iraq and Syria - though Libya, Yemen, Somalia, and (perhaps more loosely) Nigeria cannot be forgotten. In due course, who knows where else.

A process it is and a process it will remain, at least as long as the “far enemy” in the west sees it as a military operation. For the al-Qaida idea, in whatever form it may take, now and in the future, “bring it on” is a fundamental impulse. Long may the west seek to regain control, is its belief, for in that case the outcome is certain.