They couldn’t keep away. Barely two years after US forces were withdrawn from Iraq, they’re back in action. Barack Obama has now become the fourth US president in a row to launch military action in Iraq.

We’re now into the sixth day of US air attacks on the self-styled Islamic State, formerly known as Isis – the sectarian fundamentalists who have taken over vast tracts of Sunni Iraq and are carrying out vicious ethnic cleansing against minorities in the north.

The media and political drumbeat is growing louder for Britain to move from humanitarian aid drops to join the military campaign. France has announced it will be arming Iraqi Kurdish forces. There are already 800 US troops back on Iraqi territory.

Without a trace of irony, Colonel Tim Collins, who famously claimed on the eve of the 2003 invasion that British troops were occupying Iraq to “liberate” it, yesterday led the call for yet another military intervention.

If ever there was a case for another Anglo-American bombing campaign, some say, this must surely be it. Graphic reports of the suffering of tens of thousands of Yazidi refugees on Mount Sinjar and the horrific violence that has driven the Christians of Qaraqosh from their homes have aroused global sympathy.

The victims of this sectarian onslaught need urgent humanitarian aid and refuge. But the idea that the states that invaded and largely destroyed Iraq at the cost of hundreds of thousands of lives should claim the cause of humanitarianism for yet another military intervention in Iraq beggars belief.

If the aim were solely to provide air cover for the evacuation of Yazidis from Sinjar, there are several regional powers that could deliver it. The Iraqi government itself could be given the means to do the job – something its US sponsors have denied it until now. In fact, the force that has done most so far to rescue Yazidis has been the Kurdish PKK, regarded as a terrorist organisation by the US, EU and Turkey.

But after decades of lawless unilateralism, any armed intervention for genuine humanitarian protection clearly has to be authorised by the United Nations to have any credibility. As the Labour MP Diane Abbott put it, that’s what the UN is for – and authorisation could be quickly agreed by the security council.

But of course it’s not just about the Yazidis or the Christians. As Obama has made clear, they’re something of a side issue compared with the defence of the increasingly autonomous Iraqi Kurdistan – long a key US and unofficial Israeli ally – and American interests in its oil boom capital Irbil, in particular.

The US is back in Iraq for the long haul, the president signalled, spelling out that his aim is to prevent IS establishing “some sort of caliphate through Syria and Iraq” – which is exactly what the group regards itself as having done.

The danger of the US, Britain and others being drawn again into the morass of a disintegrating state they themselves took apart is obvious. IS, then known as al-Qaida in Iraq, itself effectively arrived in the country in 2003 on the backs of US and British tanks.

The idea that the states responsible for at least 500,000 deaths, 4 million refugees, mass torture and ethnic cleansing in Iraq over the past decade should now present themselves as having a “responsibility to protect” Iraqis verges on satire.

The majority of Iraq’s million-strong Christian community was in fact forced out of the country under US-British occupation. The state sectarianism that triggered the Sunni revolt and rise of IS in Iraq – the ultimate blowback – was built into the political structures set up by George Bush.

Britain and the US – which didn’t want to “take sides” when Egypt’s coup leaders carried out one of the largest killings of demonstrators in a single day in history last summer – are the last countries on Earth to bring humanitarian relief to Iraq.

That doesn’t mean that they don’t have a responsibility to provide aid. But the record of western humanitarian intervention over the past two decades isn’t a happy one. In 1991, no-fly zones in Iraq allowed massacres of Shia rebels in the south and only functioned with thousands of troops on the ground in Kurdistan, followed by 12 years of bombing raids.

In 1999, Nato’s air campaign in Kosovo, also without UN authorisation, triggered a massive increase in the ethnic cleansing it was meant to halt. In Libya, in 2011, Nato’s intervention ratcheted up the death toll by a factor of about 10 and gave cover for rampant ethnic cleansing and indiscriminate killing. Its legacy today is complete state breakdown and civil war.

It might be said that the latest US bombing campaign in Iraq has greater legitimacy because the Iraqi government appealed for support. But it did so back in June, after which Obama stayed his hand until the prime minister, Nouri al-Maliki, could be replaced with someone more acceptable to the US.

At the same time, US arms are now being supplied directly to Kurdish forces, independently of the central government, fuelling the disintegration of the Iraqi state. And IS – whose sectarian ideology is in reality only a more violent version of the Saudi regime’s, the west’s most important ally in the Arab world – is consolidating its hold on western Iraq and eastern Syria, where it is in effect allied with the US and its friends.

Its rise is a tragedy for both peoples. But another round of US and British military intervention would only strengthen IS and boost its credibility – as well as increase the risk of terror attacks at home. The likelihood is that it can only be overcome by a functioning state in both Iraq and Syria. That in turn demands a decisive break with the sectarian and ethnic politics bequeathed by a decade of war and intervention.

The urge to play the role of self-appointed global policeman retains its grip on the western world, but experience shows that will do nothing to rescue the people of Iraq. Far more important would be agreement between the regional powers, including Turkey and Iran, on a settlement to allow Iraq to escape from its existential crisis.

Selective humanitarian intervention without UN and regional authorisation is simply a tool of power politics, not solidarity. To imagine that the solution to the disastrous legacy of one intervention is to launch yet another is delusional folly.

Twitter: @SeumasMilne