What are the rules of war?
France has declared war on al Qaeda. But what does that mean - and how does a country fight a war in the modern world?
The French announcement, by the country's prime minister Francois Fillon, comes after 78-year-old hostage hostage Michel Germaneau, abducted in Niger, was killed by the network.
In particular, it is the group's North African branch that the French will target. But how does a country's or a coalition's army go about defeating a loose organisation like al Qaeda?
As the current Nato operation in Afghanistan has shown, attempting to defeat the organisation is no easy task. This was particularly highlighted by Monday's release on Wikileaks of 91,000 documents relating to that conflict, which seemed to suggest the operation was struggling to succeed and had brought about far higher civilian casualties than was being reported.
So what are the rules of war now?
Afghanistan has been a long conflicts against an enemy that crosses borders around the world, in remote and hostile locations. Any French operation in North Africa is likely to run into precisely the same difficulties.
"Given the increased resources that al-Qaeda in the Islamic Maghreb has obtained in the last 12-18 months, because its southern command has acquired resources through an alliance with drug smugglers and other criminal elements, you are seeing greater activity and, unfortunately, you are likely to see increased activity from them."
Tituswille on Twitter was immediately sceptical:
France declares to be at war with Al Qaeda! With no soldiers,no informational and strategic backup, Sarkozy can only fights the ghosts !
So, how to fight a modern conflict against a hidden enemy? Well, the Wikileak documents suggest that the approach in Afghanistan is failing to be effective. As the BBC's North America editor Mark Mardell put it:
[The reports] suggest a war conducted by secret forces, dogged by the behaviour of Pakistani intelligence, marred by constant civilian casualties, where anything resembling victory is elusive.
Meanwhile the records log 144 incidents involving Afghan civilian casualties, including 195 fatalities, the UK's Guardian newspaper reported.
What happens to civilians in conflict is one of the key aspects of the Geneva Convention - an agreement between countries of a standard for the treatment of victims of war, monitored by the ICRC (International Committee of the Red Cross).
The use of weapons is not covered by the Geneva Conventions - it is instead controlled by The Hague Convention - although a protocol called The Geneva Protocol to the Hague Convention, which permanently bans the use of chemical and biological warfare.
But there are controversial loopholes. One is that under international humanitarian law, the chemical white phosphorus - which can cause horrific burns - can legitimately be used as an "obscurants" to hide military operations and, in certain circumstances, as a weapon.
One example of the difficulties around this was highlighted last week when Israel announced it would limit the use of white phosphorus - after it was criticised by the UN and Human Rights Watch for deploying the chemical in densely-populated areas during Operation Cast Lead - the 22-day assault on Gaza which began in December 2008.
How can modern conflicts be fought? What should be the new rules of engagement - if any? Do the Geneva and Hague conventions need to be updated? And how can civilians be protected?