Situation at the beginning
Syria was established by the Entente - later the League of Nations Mandate for Syria and Lebanon, France as colonial power - with artificial boundaries, after the Ottoman Empire collapsed as a result of World War 1. Thereby the concerns of several local ethnicities (occasionally members of different faiths) have been ignored. There is a civil war since March 2011: The regime, several opponents of the regime, Daesh and Kurds fight each other.
From a present-day perspective its impossible to patch this torn nation to a new artificial state. The Israeli Secretary of Defense compared Syria with an egg, which became an omelet, that cannot be transformed to an egg again (analogously Sputnik News online from 21.07.15).
There are parallels to the Bosnian War in the 90s. At that time the three fractions (catholic Croats, orthodox Serbs and muslim Bosnians) tried to conquer soil as much as possible. Shortly before the end of the war and during the peace talks the warring parties were still fiercely fighting in order to gain more soil and negotiation power. Especially this war has shown, that a civil war can rapidly turn into a proxy war.
And like Bosnia in those days, Syria became a pawn in the hands of the great powers. American and European (more precisely, France and England) military is involved in Syria in order to avoid the increasement of the threat of terror in the world. However, some other great powers are also present in Syria: namely Russia, Turkey and Iran. Officiallyall these intervening great powers work hand in hand and have common goals. Unofficiallyeach nation pursue its very own national interests. The prioritization of combatting opponents is different for each of them, as you can see in the following list:
Daesh: This group has no allies and is opposed to all the other groups. It fights against PYD, the moderate regime opponents and the regime. Daesh finances the war by smuggling antiques and raw materials. These fanatics dream of the world conquest as a long-term goal.
PYD (Kurds): Is categorized as terrorists by Turkey. Therefore Turkey combats that group particularly. Kurds fight for autonomy or independence. They control almost the whole borderland to Turkey like a bulwark. USA and Europe support them with arms and trainings, because the mastery of the region along the border should prevent Daesh members spread from Syria via Turkey to the world.
Regime (Syrian President): Combats halfheartedly Daesh, leaving the work to the Kurds and the coalition. The president has obviously accepted the loss of the northeastern areas of his country. For that reason the focus of his army is oriented to the enemies in the northern area (Turkmen and other opponents of the regime).
Regime opponents: Are in struggle against the regime, PYD and the Russian forces. Their area doesnt have a front line to Daesh. The Turkmens are one of several fractions among the opponents of the regime. They enjoy the support of Turkey, which sees itself as their protecting power.
Russia is involved actively in fightings in Syria since 30.09.15. The Syrian regime allows Russia to operate some military bases on Syrian soil. These are the only military bases of Russia that are located outside the former Soviet Union and the Arctic Zone; nearby warm waters. As long as those bases are in operation, Russia can exert influence on the international Near East policy. OfficiallyRussia intervenes in the civil war to fight Daesh. Unofficiallythe friendly regime is to be strengthened by fighting their enemies.
It was only a matter of time that an accident or a collision happened among the foreign powers in Syria: On 24.11.15, two Russian tactical bombers of type Sukhoi Su-24 violated the Turkish airspace for a few seconds. As a result one of them was shot down by a Turkish multirole combat aircraft of type F-16. Prior to this incident, the Russians already violated the Turkish airspace. At that time they apologized. This time Russia denied that its aircraft violated Turkish airspace again.
Russia and Turkey have been maintaining markedly good relations until the downing. Turkish bathing places were very popular to Russian tourists. Over the past decade, the number of Russian residents in Turkey increased relatively strong. Many mixed marriages came about. Hereby the cultural exchange between both nations experienced an upswing. They have been adapted commercially through joint large-scale projects, such like the construction of Turkey's first nuclear power plants and the construction of the Turkish Stream pipeline. Additionally the Blue Stream pipeline is in operation since 2003. Many Turkish building enterprises are present in Russia. Even the formation of the Turkish nuclear physicists, who are proposed to be appointed in the new nuclear power plants, takes place in Russia. The EU sanctions against Russia contributed to increased food imports from Turkey to Russia. Both countries already traded on a grand scale with chemical products, automotive parts, machines, etc.