A snap war is a grave mistake
The beheading of two American journalists and a UK aid worker brought home to the western world the barbarous nature of the Islamic State (IS) terror group. The murders also brought an emotional response from people in many countries who demanded military action against IS.
But governments cannot, and should not, take decisions based on emotion.
They must weigh up what can be done and what the possible consequences of any action will be.
That is what MPs must do today when they vote for military action against IS in Iraq. Any military campaign is fraught with danger, especially if undertaken in haste.
It is already worrying to hear suggestions of a long-running air war against IS.
MPs should insist on more clarity before they sanction this military campaign.
And then it should be as short as possible, with the option to review how it is going after a reasonable period of time.
Very often, what is promised to be a short, sharp campaign drags on interminably with no long-term gains visible.
The Government must also make it clear that it has an exit strategy. The UK should not be afraid to set its own agenda, and it should not be swayed by US or any other country's interests.
To go into Iraq again, albeit in the air, without a strategy on what it wants to achieve and in what timeframe would be disastrous.
This military action cannot be taken in isolation. David Cameron, to his credit, has been active in trying to broaden the coalition of countries willing to engage IS.
There certainly needs to be more nations involved and, ideally, it should be military personnel from countries in the region who eventually take on IS on the ground, backing up the forces of Syria and Iraq.
Finally, the Government must give greater detail on the threat it believes IS poses to us.
So far, we have heard only generalities. Of course people are horrified by the barbarism of IS and want the organisation destroyed, but they remain to be convinced that this air war will achieve that.