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