Can the US “degrade and ultimately destroy” the Islamic State in Iraq and Syria, or Isis, as President Barack Obama promised on Wednesday, without being drawn into another open-ended conflict?

Not if America intends, as Joe Biden, the vice-president, put it last week, to follow Isis “to the gates of hell”. That open-ended commitment takes pressure off states in the region to solve their own problems, and acting upon it would be a strategic mistake. Americans are anyway unlikely to accept the cost in blood and treasure. That should primarily be borne by the regional states whose broken politics brought Isis into being, and which have the most to lose. Yet these states cannot realistically be expected to defeat Isis militarily without US support. Whether the US can avoid entanglement in a long war depends on how it defines its role in defeating Isis.

When western forces fought in Afghanistan in 2001 and in Iraq in 2003, they quickly defeated the armies fielded by those states. But then the west took primary responsibility for defeating the insurgencies that had taken root inside the borders of those states. The follow-on mission, which I experienced as an infantry officer in southern Afghanistan, became indistinguishable from local politics. Given the need to tackle all the problems that stoked insurgency – poor governance, corruption, land rights, ethnic prejudice – it could not have been anything less. The hard military objective of defeating an enemy evolved into an open-ended commitment to stabilise politics and civil society.