The downing of a Russian Sukhoi-24 bomber by Turkey reminds us of the risks which attend military intervention. There are, however, a number of additional complicating factors which promise to make the Syrian war even more dangerous and bloody for all sides.
Some of the facts of the matter are still murky. Russia and Turkey have released rival satellite traces. On the Russian account, the plane never entered Turkish airspace — staying at least a kilometre within Syria at all times.
If this is correct, this is a straightforward act of Turkish aggression (Russian planes fly in Syria with that country's Government's consent) and would, in days gone by, have led to a declaration of war.
The Turkish version has the Russian plane crossing Turkish airspace twice, but spending no more than 17 seconds inside Turkey.
The Russians have form, having previously admitted accidental incursions over Turkey, and the Turks have previously declared a zero-tolerance policy for further incursions. Nevertheless, even on the Turkish version, the plane was clearly shot down in Syria and international practice is to escort intruders out of one's airspace, only shooting as a last resort.
Further exacerbating the situation is the fact that Turkey's client Turkmen militia in Syria claim to have shot the pilots as they parachuted from their plane, killing at least one. This is a war crime in both customary international law and by treaty. Would-be rescuers were also shot at and at least one killed.
This could escalate dangerously. Turkey is a NATO member and article 5 of the NATO Treaty allows any NATO country claiming an act of aggression to invoke mutual defence — raising the spectre of a wider NATO-Russia war. Given that both sides are armed with nuclear weapons this would be catastrophic.
Fortunately NATO seems unwilling to provide more than verbal support to Turkey, and Russia has also restricted itself to vocal condemnation (although it has announced that future bombing missions against ISIS and other anti-Assad groups in Syria will have fighter escorts).
Behind all of this lies the overlapping great power games which bedevil the Syrian war. As is well-known, Russia regards all enemies of Assad as legitimate targets, while NATO (and Turkey, in particular) have declared a wish to see the Syrian president removed — if not as their first priority, then at least as a close second.
This has led to some uneasy alliances, with even conservative US newspapers like the New York Times and Washington Post expressing disquiet that Al-Qaeda affiliate Jabhat al-Nusra is being supported by the US as a 'moderate rebel group' now that the Pentagon's own 'train and equip' program has failed.
If the Western allies are not picky about who replaces Assad, their Gulf colleagues and Turkey are even less so. Jaish al-Fatah, an umbrella group including Al-Nusra, has long been receiving backing from Saudi and other Gulf States, and Saudi and Qatari backers have been implicated in ISIS funding.
Turkey has been supporting the Turkmen and has been accused of turning a blind eye, at best, to ISIS' activities. The fact that Russian aircraft have been targeting oil tankers shipping oil from ISIS-held fields in Syria into Turkey will not have improved relations between the two countries. The Turkish border was already relatively porous, with ISIS not experiencing a great deal of difficulty moving from side to side.
In fairness, it is not clear whether Turkey has actively been supporting ISIS or merely whether it has had other priorities.
Kurdish rebel groups, regarded by Russia, the US and Israel as reliable bulwarks against ISIS, have been fighting for their own state in the Turkey-Syria-Iran-Iraq region for years. While no friends of Assad, geography alone (ISIS has its base on the Iraq-Syria border) meant that they had been bearing the brunt of the anti-ISIS campaign.
The Turkish president, Recep Tayip Erdogan, fresh from his recent election victory on an avowedly Turkish nationalist platform, sees the Kurds as a much bigger threat than ISIS and has been prioritising his military actions accordingly: waging enthusiastic war on the Kurds (including cross-border strikes into Iraq and Syria), with only token contributions to NATO's anti-ISIS campaign.
In short, if this kind of event is not to become much more common — potentially leading to a much wider war — genuine peace talks with a lot more honesty on each side need to be a priority.
Justin Glyn SJ is studying for the priesthood. Previously he practised law in South Africa and New Zealand and has a PhD in administrative and international law.