The increasingly desperate situation in Iraq does not lend itself to easy solutions.
The advances made by the hardline Islamic State in Iraq and the Levant (Isis) have significant implications for the Middle East and in the West.
The rise of a Caliphate, a radical Islamic state spanning a large swathe of the region including large parts of Iraq and Syria, is no longer an outside possibility. It is not an outcome America and her allies can tolerate.
But preventing it is another matter. It is in the interests of the West for the government of Nouri Maliki to be supported and for the Iraqi Prime Minister to be helped to restore calm to his country. However, there is little Britain can do to achieve that.
While in hindsight, tackling the social divisions in Iraq would have been desirable, it is hard to see how this can be done now. Isis's rapid advances have been helped by a sense of grievance from the marginalised Sunni Arab community, which has either failed to resist or actively helped the radical Islamist organisation.
Paradoxically, Mr Maliki is in this sense partly the source of the problem. Redressing the disenfranchisement of Sunnis is now almost certainly beyond him, even if he were willing.
Past Western military action has also brought us to this point, of course. The Chilcott Inquiry report, when it is finally published, might shed light on the reasons behind the last Iraq war. But it has long been clear that insufficient thought was given to what should happen after Saddam Hussein was removed from power. The inability of the US to establish an Iraqi army capable of maintaining order or indeed resisting the Isis surge into Mosul is among the legacies of that.
Nevertheless, further military action by the US seems increasingly likely. While clearly left on the table by President Barack Obama and his Secretary of State John Kerry, this does not offer a straightforward solution.
With the forces of Isis relatively small in number and distributed within the population, air strikes are likely to have a limited effect. But in promising action in the region soon, Mr Kerry ruled out the use of ground troops.
Perhaps one positive is the possibility the latest conflict offers for building diplomatic relations with Iran, where the relatively moderate president Hassan Rouhani and his US counterpart suddenly have an unlikely common cause.
But there are questions to be asked about the failings of US intelligence which, despite a multibillion-dollar budget, failed to predict the threat posed by Isis, or its ability to move with astonishing speed and effectiveness to seize control of large parts of Iraq.
Having been similarly blindsided, albeit in a different way, over Crimea, questions are already being asked in the US about how such lapses can have been allowed to happen.
For now, the UK can do little other than offer intelligence and logistical support for the Maliki government and be ready to offer the same for US military muscle, should it come to that.