The Islamic State are different from AQ in that they have territorial ambitions, the clue is in the name. Their PR success is buoyed by their successes. France has the expeditionary capability to assist in driving the IS out of the territory it currently occupies.

If France doesn't care about who takes control of the territory afterwards, as long as they aren't terrorist supporting Islamists then it does have the capacity to seriously damage IS. Will it lead to world peace and happiness, no. Will it lead to an awful lot of Syrians continuing to die, yes. Will it marginally improve the lives of those suffering under IS rule, I believe so. Will it degrade IS' ability to recruit and inspire terror attacks abroad in the long run, yes.

Given a lot of poor choices you need to find the best one. Doing nothing is a conscious choice that may not be the best option.

I think the west needs to think long and hard about nation-building, not just fighting wars. They also need to have frank discussions with their nominal 'allies' in the ME who are driving a lot of the instability.

I have no doubts France has the capability to "seriously damage" Daesh, but what about Daesh's successor - which is likely to be just as bad (or worse)? Unfortunately, it seems like democracy (with it's 4-/5-year election cycles) is incompatible with long term planning. It's a mirror-image of the modern-day corporate world, with CxOs who damage the organisations they lead in the pursuit of short-term gains (and the resulting bonuses), except that election stakes are higher (keep/lose the job).

IS' successor would not be a territory holding aspirant state, it would have to be more like AQ - which we have already significantly degraded.

Now there is the interesting concept of the rise of the "lone wolf" or individual cells that don't really have central co-ordination. Would Western intervention in Syria cause more of them? Would their rise be countered by reducing or removing the ability of IS to generate attacks? There's a debate to be had.

I am afraid the answer to all of those questions is NOPE. ISIS did grow and will continue to grow as long as there is foreign military existence on Middle-east soil. It is extremely easy to recruit people to do anything while their national/religious pride is being pissed on by their historical enemy.

IS grew out of the vacuum of a civil war in Syria and is predicated on creating a Caliphate. They cannot physically grow if they are not able to gain ground. Their recruitment message is likely to be significantly weakened if they lose territory and battles. Unlike AQ or even the Taliban of recent years they are not able to avoid pitched battles, they can't melt into the background - they would have to stand and fight for their territory - thus they can be defeated.

They can definitely hide in the population. Rakka still have 200,000 people living there. I have no idea which part of that population are hardcore isis member : 40-50k maximum maybe. Assuming you could take Rakka, you can't just execute or deport every one with a weird accent. Mosul is even bigger.

How many ground troop would it take to occupy all these cities ? This would be a repeat of the second Irak war, or Afghanistan, with the endless terrorist attacks, IEDs, etc.

Even if you have contributions from Kurds, Irak regular army, or Hezbollah, they would not be welcome as savior in Sunni's territory.

Like in most conflict, the military option can be used to create conditions for a political resolution, but you have to provide some sort of long term plan for Sunni population : you can't just tell them they will go back under Assad rule they despise in the first place. Currently, I don't believe there is a clear political solution. In this condition, the military option is doomed to fail.

My earlier post posited not caring, let the civil war continue, hand it over to the "nicest" Sunni group we can live with, give it to Assad - none of those outcomes involve a terror exporting aspirant state controlling territory. If we temporarily control a swathe of territory it puts in a position to make a bargain with someone.

I'm not saying it is good, but is it better than a pretty shitty situation. Do the other groups regularly crucify civilians and hurl homosexuals off buildings? If we acknowledge we can't impose a new government can we create a new normal whereby we smack groups which get out of line but otherwise stay out of the way. It's actually fairly similar to the old Roman system on the outskirts, and the same approach the British initially adopted in the early days of Empire. It's what the Americans sort of did in Afghanistan before the invasion of Iraq effectively dragged them into a civil war.

In some sense, France already does this type of thing in Africa. Most recently in Mali.

Not sure in which way Syria would be significantly different.

Also, Russia is being pulled even more into Syria. So a truly international force may materialise at some point. Not that I'm advocating that's a good thing.