Here are five inconvenient facts for those who believe there is a simple military solution to Syria
1. There are very few 'good guys' to back
ISIS and the Syrian regime have few military opponents. Dozens of militias crowd the battlefield, their allegiances as impenetrable as they are varied. It's a mess -- but a few players stand out, often for bad reasons.
The biggest Sunni Arab force against them is called Jaish al-Fateh. It's an alliance that includes moderates, those who are increasingly radical (such as Ahrar al Sham which, despite being termed "radical" by the U.S. State Department, nevertheless condemned the Paris attacks), and al Nusra Front, al Qaeda's affiliate in Syria.
This alliance -- which had seen such great success against the Assad regime that it prompted many to think the Russian intervention was intended mostly to slow its advance -- has itself faltered.
For a while, Jaish al-Fateh stopped operations when one part of the alliance disagreed over its anti-ISIS stance.
Meanwhile, the groups the West used to call "moderates" have been sidelined and underfunded and are tiny. The New Syria Force, which was the product of the Pentagon's $500 million Train and Equip program, produced 54 fighters. Defections and clashes meant at one point the force only had five fighters left.
The other moderate force, the Syria Democratic Front, is also small and poorly supplied. Critics dismiss it as a fig-leaf group of Sunni Arabs to make the Kurdish forces they fight alongside seem more multiethnic.
Result: There aren't many pro-U.S. forces in Syria right now. The Assad regime now has fighting alongside it Hezbollah, which the U.S. considers a terrorist organization, and the Iranian militia, which fought the U.S. in Iraq. Al Qaeda is the most militarily effective part of the main anti-Assad regime alliance. Then there's ISIS. Many look to the Kurds as the best allies against ISIS , but ...
2. The Kurds? They aren't the solution to everything
The Kurds are sometimes mistrusted by the main group the U.S. badly needs to court: Sunni Arabs. They, in both Iraq and Syria, are the ones whose disillusionment with the Alawi and Shia regime in Damascus and the Shia-dominated government in Baghdad gave ISIS the oxygen to exist.
When the Assad regime bombed Sunni civilians at the beginning of the Syrian conflict, then continued daily for years, al Qaeda and then ISIS presented themselves as their protectors.
Sunnis are a minority in Iraq but a majority in Syria. Without their trust and cooperation, you can't expect to kick ISIS out. And the Sunnis don't trust the Kurds. The Kurds in Syria have cooperated with the regime from the start -- or at least agreed not to fight each other.
And the Kurds are most interested in creating their own homeland in northern Syria, which they call Rojava. That means that when they liberate lands from ISIS, it can't immediately be guaranteed that they will welcome back the Sunnis who used to live there.
Even in Iraq it's a problem: A Kurdish commander I met outside Sinjar last week said he felt all the Sunni Arabs around that area were ISIS supporters.
The upshot of this mistrust is an impediment for those who advocate using the Kurds as a ground force against ISIS. You can't expect to attack Raqqa, a Sunni Arab city, clear ISIS out and then be able to administer a large, angry Sunni population. Advocates of the Kurds say they can, and point to the fact that all the sides against ISIS are Syrians and have lived together in the past. But it will be a challenge.
You need Sunni Arabs -- and there are very few the U.S. wants to work alongside.
3. Turkey is part of the problem, even though it's in NATO
It was the Turkish failure to stop jihadists flooding into Syria in 2013 that enabled ISIS to grow. The Turkish-Syrian border remains porous and the Turks are, many say, more interested in fighting the Kurds in Turkey, Iraq and Syria, whom they consider terrorists, than they are in combating ISIS.
This has changed since ISIS attacked Ankara, the Turkish capital, in October and has become all the more violent in southern Turkey.
But it took the U.S. months to negotiate the use of the Incirlik airbase in southern Turkey to bomb Syria and Iraq. This was an advantage that Washington badly needed in order to reduce flight times and increase sorties -- yet the holdup came even while negotiating with a NATO ally.
Unless the border with northern Syria and Turkey is sealed, ISIS can continue to resupply its "caliphate" with new recruits and send attackers toward the West. Sealing that 900-kilometer (560-mile) fence is an essential start -- but it has not happened yet.
4. Obama's strategy sounds tired and compromised -- but it may be the best option
At the G20 meeting in Antalya, Turkey, this week, the commander in chief of the world's most powerful military sounded a lot like he was justifying his policy of airstrikes and special forces advisers teaching local militia -- a policy that few thought was working.
But U.S. President Barack Obama's challenge to people to present serious and effective alternatives was sound.
After Iraq and Afghanistan, an indefinite military occupation of hostile territory is unlikely to sit well with the American public -- however viscerally satisfying an idea it sounds to politicians on the stump.
Airstrikes and special operations forces strikes do eventually wear down insurgencies, as we saw in Afghanistan. Some Western officials accepted that the nightly raids against the Taliban were actually too effective, destroying the command structure and ensuring there were too few leaders left to talk to and calm down the young insurgents doing the fighting.
Obama says it will take time, and that is unacceptable to both Parisians seeking retribution and Americans wanting the U.S. to retain its leadership role in vanquishing terrorists.
But the President's challenge for clear alternatives has yet to be coherently answered. The White House has dealt with this reality for years, first by ignoring it, then by trying to stay out of it, even when its red lines over chemical weapons were crossed, and now by trying to contain it.
The time for an easy intervention was in 2012, before ISIS, when the rebellion in Syria was moderate and the Assad regime not supported so strongly by Iran and Russia. Now things are different. They just are. It's too late.
5. There needs to be a local solution for what is a regional proxy war
ISIS is a radical, nihilistic organization using the vacuum of chaos in Syria and Iraq to find a haven. That chaos is caused by the broader battle between Iran and Saudi Arabia (often with other Gulf states) vying to establish supremacy in the region.
Both nations have aging leadership, huge young populations and crashing incomes from low oil prices, and as a result see sweeping changes ahead in the region. Each seeks to get ahead of the other as quickly as possible.
But in Iraq, the West has shown that it is pretty useless at invading, remodeling and then administering a Middle Eastern country. Saudi Arabia and Iran know this and don't see that as a real prospect in the future.
The U.S. diplomatic strategy also recognizes this regional showdown, hence its focus at U.N.-administered peace talks in Vienna on getting Saudi Arabia and Iran to sit in the same room and agree on basic points about Syria's future.
The latest consensus even saw the U.N., U.S. and Russia all state that the backers of the various warring groups in Syria would make their proxies respect any U.N. ceasefire initiative. It's all very distant and optimistic as a prospect, but it does tackle the issue at its root cause: at the level of the Syrian militias' backers, rather than militarily on the ground.
In short, the region itself must get tired of the war and the chaos and seek to negotiate an end, as the West isn't going to be able to impose one.
Is there any good news?
One small historical comparison to ISIS is the Khmer Rouge.
That regime didn't attack the West, granted, but it was equally nihilistic and savage during its brief rule in Cambodia, after the turmoil of the Vietnam War.
After years of horror, the Khmer Rouge did eventually find itself isolated, unable to basically feed the populations it brutalized, and slowly collapsed as a result.
That takes time, as Obama says -- and that's not something those on the streets of Europe's capitals want to give ISIS right now.