The jihadis of Isis are coming under severe military pressure. In Iraq, their western stronghold of Falluja looks set to fall while Baghdad, backed by US air power, has started the campaign to retake the northern city of Mosul, captured by Isis two years ago in the lightning cross-border strike from Syria that linked up the territory of its self-declared caliphate.

In northern Syria, US-allied forces are pressing down towards the Isis capital of Raqqa, and threatening the jihadis’ last funnel to the outside world at Turkey’s border west of the Euphrates. Is the caliphate cracking? Will President Barack Obama succeed in evicting Isis from Raqqa and Mosul before he leaves office?

In military terms, these developments look promising but far from concluded. There are too many actors pursuing different goals, and Isis has proven power to strike back even in retreat. Yet even if these operations all go swimmingly, the politics on and off the battlefield are so unpromising that it is hard to envisage a definitive Isis defeat. We have seen this movie before.

The al-Qaeda precursor of Isis came close to military extinction after the US-led “surge” of 2007-08 in Iraq. The jihadis came back stronger than ever within five years. The decisive weapon in the surge was the Sahwa (Awakening), a 100,000-strong coalition of Sunni fighters that turned on al-Qaeda for brutally usurping the prerogatives of the tribes. The Sahwa was subsequently marginalised, disbanded and then persecuted by the Shia-dominated government in Baghdad, which saw it as an armed threat to its sectarian power. The jihadis were back in business.

The conflict in Syria, where the Sunni majority felt ever more betrayed by western failure to provide support to mainstream rebels against the onslaught of Bashar al-Assad’s regime, provided Isis with an ideal vacuum in which to regroup and the springboard back into Iraq. In both countries, the Sunni have been driven towards Isis, and more diluted variants of jihadism backed by Saudi Arabia and Turkey.

What is the position now? As Iraq’s regular forces move further into Falluja, escaping Sunni civilians are being ground between two stones. Isis is killing people trying to escape, while hundreds of those who succeed are being tortured as suspected jihadi fifth columnists by Shia militia forming the outer ring of the siege and insulation against suicide bombers who have been causing carnage in Baghdad. In Syria, many Sunni Arabs fear the territorial ambitions of Syrian Kurdish militia, the most effective US-allied strike force against Isis. In Raqqa, Isis is slaughtering by the score those it identifies as waverers. Russian- and Iranian-backed Assad regime forces are also pushing towards Raqqa, even if their main focus remains to eliminate non-Isis Sunni rebels.

Many hundreds of thousands of ordinary Sunni, in other words, are trapped between tyranny and terror, the sectarianism of Damascus and Baghdad or the savagery of the Isis brand of Sunni supremacism. And that is to oversimplify. What exists is a crazy kaleidoscope of colliding and recombining microcosms across a shape-changing battlefield, with no overarching political narrative that might change this. That spells defeat insofar as any attempt to eliminate the threat of Isis requires a strategy to mobilise, secure and turn Arab Sunni sentiment against it.

“Even if the different actors in the war make the Islamic State [Isis] their main target, they will still need the local population to reject the group if they hope to fully defeat it,” argues Fabrice Balanche, a French scholar at the Washington Institute, in a recent paper describing the numbing complexity of highly contingent tribal affiliation.

This is almost matched by the complex interplay of external actors. Russia seized the initiative in Syria last autumn when the Assad rump state looked as though it might succumb, but its primary objective is to reassert its superpower credentials. Iran, despite the opportunity to rejoin world markets and councils after last year’s deal with international powers on its nuclear programme, still behaves as if its priority is to strengthen the Shia Arab axis it has forged from Iraq through Syria to Lebanon.

The focus of the US, its regional influence in decline after the bloody fiasco that followed its 2003 invasion of Iraq, and Mr Obama’s decision in 2013 not to act against the Assad regime after it crossed his “red line” and used nerve gas against a rebel enclave, seems circumscribed to the military effort against Isis. Of its main regional allies, Turkey is obsessed with preventing further Kurdish gains in Syria, while Saudi Arabia’s first and last concern is countering Iran in the region.

Isis may keep losing territory. But unless the US and Russia from outside, and Saudi Arabia, Iran and Turkey from inside the region, can agree to chart some sort of political course together, it is hard to see it being expunged from the Sunni world.