Female members of the Armed Forces of the Philippines and the Philippine National Police wait to board a plane at the Villamor Air Base in Pasay City Aug. 29, 2017. The female troops will be sent to Marawi City in south Philippines. Rouelle Umali/PA Images. All rights reserved.

In the past month, ISIS has suffered serious reversals in Iraq and Syria. The Baghdad government, with essential help from the United States-led air-power coalition and Iran, has consolidated its control of most of the former ISIS-held territory. But the prolonged onslaught on Mosul saw its special forces taking severe casualties, which improves ISIS's chances of being able to move into a guerrilla war. In turn that will oblige even greater reliance on Iranian support. That is but one of the ironies in Iraq's long conflict, which Washington launched in 2003 against Saddam Hussein's regime partly to curb Iranian power in the region.

The related war in Syria has its own twists. ISIS there is under pressure from two alliances: of Kurdish-plus-western forces and Syrian army-plus-Russian. There is now little talk in western capitals of the Bashar al-Assad regime being soon ousted, in spite of all its brutality and use of chemical weapons. Turkey is concerned about the increasing power of the Syrian Kurds as well as Assad's survival, while the Saudis and their western Gulf allies fear the “Shi’a crescent” stretching from the Mediterranean to the Arabian Sea through Lebanon, Syria, Iraq and Iran.

Against this, though, western capitals are tempted into cautious optimism that the war against ISIS might at last be coming to an end. Whatever the problems and complexities now emerging, at least that particular one is receding. Or is it? For at each stage in the "war on terror", the same positive outlook has emerged, only to be dashed by events.

The pattern was set soon after 9/11, when the Taliban regime in Kabul was terminated, al-Qaida dispersed, and Osama bin Laden and Mullah Omar went underground. These advances led President George W Bush, when he delivered his state-of-the-union address in January 2002, to proclaim a global fight against an "axis of evil" which the United States would prosecute with determined force. Sixteen months later, the termination of the Saddam Hussein regime in Iraq allowed him to reprise the cheerleading in his “mission accomplished” speech. A decade on, under Bush's successor Barack Obama, the killing of bin Laden and the overthrow of Muammar Gaddafi's regime in Libya brought another cycle of optimism.

These precedents advise a considerable degree of caution. This week, as the US and the world enter the seventeenth year of the "war on terror", a third US president – Donald J Trump – faces its grim product. Miltary reinforcements for Afghanistan are being weighed as Taliban influence grows, Libya is chaotically insecure, Iraq is divided and violent, Iran is ascendant in the region, and ISIS-inspired attacks in western states continue. Meanwhile, the third member of that "axis of evil" – North Korea – is more defiant than ever.

A tale of two presidents

Amid these urgent challenges is a host of lesser but still serious ones which may also have long-term implications. A neglected example, in western media at least, is the violence in the southern Philippines, especially the city of Marawi on the island of Mindanao.

Islamist paramilitaries seeking autonomy for the south, a wider political goal, had been active for more than a decade and even came quite close to a peace agreement with the Manila government. Some, though, took a harder line. When ISIS made its spectacular gains across Iraq and Syria in 2014 the leader of the Abu Sayyaf group, Isnilon Hapilon, pledged allegiance to the emerging movement. After two years' organising, he succeeded in 2016 in uniting several paramilitary groups.

Duterte’s government failed to recognise the developing power of this enlarged cohort. Its early efforts at suppression failed, and in May 2017 a cell of Islamist paramilitaries claiming links with ISIS took control of key parts of Marawi. This might have been more of a gesture intended to last just a few weeks. In the event, the paramilitaries found it easier than expected to hold on to much of the city, as the Filipino army – more used to rural counterinsurgency – proved incapable in urban warfare against determined rebels prepared to die for their cause.

The United States poured in special forces, navy surveillance planes, and other units. There were near-weekly predictions that liberating the city was at hand. But the early confidence that the Islamists would soon flee or be killed proved unfounded By mid-June there was growing evidence that Duterte’s troops were relying heavily on air-power and artillery, which limited the rebels’ hold but severely damaged the city and killed many civilians in the process. Analysts further highlighted the Filipino forces' poor intelligence capabilities.

Only now, four months after the conflict started, are there signs that those rebels who have not been killed may be leaving Marawi. The costs are immense. In "a city of 200,000 residents that has been transformed into a moonscape by almost daily bombardments by government forces”, scores of civilians have been killed, many more wounded, and 400,000 people displaced.

This outcome provokes acute fear in both Manila and Washington that the Islamists' unexpected success in prolonging the conflict will encourage them to diversify their strategy. Behind Duterte's well-known bluster, the weaknesses of his army have been revealed. There are now real concerns that the rebels will focus on other urban areas, and perhaps even move to metropolitan Manila itself. Moreover, there are indications that other Islamist groups in the Philippines are linking up to aid allied groups in Malaysia.

In that case, the other boastful president involved in the Philippines crisis will face a real dilemma. The Pentagon used to provide support for Manila's armed forces through the US's Joint Special Operations Task Force – known as Philippines (JSOTF-P) – but this was stood down two years ago. Trump may well come under pressure to allow it to be operational again, not least because of indications that Islamist groups elsewhere in the Philippines are linking up to aid allied groups in Malaysia.

In short, just as ISIS is retreating in what remains of its caliphate in the Middle East, it now sees the Philippines as a potential hub for expanding operations in southeast Asia ­– including Malaysia and Indonesia. The end of a movement with no single centre and many affiliates may not, after all, be so near.