The key fact is the Russian plane, by Turkey's own admission, was in Turkish airspace for precisely 17 seconds. That's a little less time than it takes to read this paragraph aloud. The Turks shot it down anyway -- and their allies publicly backed them, as loyal allies must.

NATO Secretary General Jens Stoltenberg declared: "We stand in solidarity with Turkey and support territorial integrity of our NATO ally, Turkey."

President Barack Obama called his Turkish counterpart, Recep Tayyip Erdogan, to assure him the U.S. supported Turkey's right to defend its sovereignty. But privately, they must have been cursing Erdogan. They know what he's up to.

This is the first time in more than 50 years that a NATO plane has shot down a Russian plane, and it happened in very suspicious circumstances.

Even if Turkish radar data is to be believed, the two Russian SU-24s only crossed the bottom of a very narrow appendix of Turkish territory that dangles down into Syria. As Russian President Vladimir Putin said: "Our pilots, planes did not threaten Turkish territory in any way. " What harm could they have done in 17 seconds?

According to Russian radar data, it was the Turkish planes that crossed into Syrian territory. In this version of the story, the Russian planes were following a well-established route just south of the Turkish border, probably turning into a bomb run against Syrian rebels in Latakia province. How strange there was a Turkish TV crew in northern Syria, positioned just right to film the incident. (The Russsian plane crashed 4 km. inside Syria.)

Either way, it seems clear President Erdogan really wanted to shoot down a Russian aircraft, and the Turkish pilots were under orders to do so if they could find even the slightest pretext. So why would Erdogan want to do that?

President Putin said bitterly Erdogan and colleagues were "accomplices of terrorists". That's hard to deny: Erdogan is so eager to see Syria's President Bashar al-Assad overthrown he left the Turkish-Syrian border open for four years so recruits and supplies could reach Syrian rebel groups, notably including Islamic State (IS).

Erdogan is determined Assad must go. But he also wants to ensure there is no new Kurdish state on Turkey's southern border.

The Syrian Kurds are the US-led coalition's only effective ally on the ground against IS.

When Erdogan committed the Turkish air force to the Syrian war in July, he explained it to the U.S. as a decision to fight Islamic State, but in fact Turkey has made only a token handful of strikes against IS. Almost all Erdogan's bombs have actually fallen on the Turkish Kurds of the PKK and above all on the Syrian Kurds

Erdogan has two goals: ensure destruction of Assad's regime, and prevent creation of a new Kurdish state in Syria. He was making progress on both -- and then along came the Russians in September and saved the Syrian army from defeat, at least for the moment.

Worse yet, Putin's strategy turns out to quite pragmatic, and even rather attractive to the U.S. despite all the anti-Russian propaganda by Washington. Putin wants a ceasefire in Syria that will leave everybody where they are now -- except Islamic State, which they can all then concentrate on destroying.

This strategy is now making headway in the Vienna ceasefire talks, but it is utterly abhorrent to Erdogan because it would leave Assad in power in Damascus, and give the Syrian Kurds time to consolidate their new state. How can he derail this Russian-led project?

Well, he could shoot down a Russian plane, and try to get a confrontation going between Russia and NATO.

Gwynne Dyer is an independent journalist based in London, England