The US and much of the world have been rudely awakened to the fact that the group formerly known as Islamic State in Iraq and the Levant is both a dangerous terrorist organisation, and considerably more than that. The deadly reality of its capabilities and ambitions is captured in the latest title by which Isis styles itself: the Islamic State. It is a de facto government with evolving borders that seeks to impose its vision of society on the millions of people over whom it rules. And, as it has dramatically shown since the capture of the Iraqi city of Mosul in June, it seeks to expand its borders and the numbers subject to its control.

The biggest question now facing western states is what to do about Syria. Iraq’s neighbour is where Isis established itself and from where it directs its operations. The fact is that the world cannot defeat Isis in Iraq, or limit its potential elsewhere, if it continues to enjoy sanctuary in Syria. Yet this is a country whose president, Bashar al-Assad, stands accused by the west of war crimes as part of an onslaught against his own citizens that has fuelled a conflict costing almost 200,000 lives.

The first thing that needs to be done, despite White House reluctance, is to make good on what General Martin Dempsey, chairman of the US joint chiefs of staff, suggested last week. The US should attack Isis targets across the border from Iraq inside Syria. More could and should be done, too, to slow the flow of recruits, arms and dollars.