War planning: Now in Theory
If a Russian jet had been accompanied by fighter aircraft, it is unlikely that Turkey would have decided to shoot down the Su-24 on the 24th of November. The transfer to Syria of S-400 air defense systems could have also taken place sooner. The consequences of military operations is always fraught with unforeseen effects, even with a weak opponent. The fog and friction of war, as Clausewitz explained, is relevant in the 21st century too, even with precision weapons and new methods of intelligence.
The interests of the global hegemon
First of all, war is profitable for the US. They are far from Europe and can use it for their own purposes - the military industrial complex (MIC) supports the US economy. Moreover, Washington finds that it is advantageous to restructure the greater Middle East to their needs. Stepping in at the last stage (as was the case in the WWII), the United States will qualify for the role of one of the winners, regardless of the outcome of the war. A number of political forces (neo-conservatives, the liberal interventionists, pro-Israel lobby) in the United States are actively trying to exploit this issue.
War, under the auspices of NATO, is a danger for Russia. However the possibility of this is also not clear. Several European countries will not support Turkey's request for assistance. In particular, Greece will come on the side of Russia. Previously, Turkey has repeatedly violated Greek airspace. In 2014 alone, Turkey was documented violating Greek sovereign airspace 2244 times. In addition, EU Member States have their own reasons to punish Turkey for the influx of migrants to Europe which passed through its territory. Therefore, even a discussion within NATO about supporting Turkey will create friction between members of the alliance.
Direct and indirect actions
Russia may use economic leverage. Cutting off supplies of gas and oil to Turkey will be come prior to military action. In addition, the Russian side will play Armenia, where a Russian military base is located. Russian support of Kurdish separatists in Turkey will lead to a civil war on the territory of Turkey itself.
For its part, Turkey will block the Bosphorus and provide military bases for US troops. Ankara also will actively support Ukraine against Russia.