Turkish F-16 fighter jets or drones would not have entered Syrian airspace — where Syrian, Iranian and Russian defenses are stacked — had Ankara not felt confident that they were under the protection of American forces there.
Furthermore, Russia, which gave Israeli fighter jets the freedom to bomb Iranian and Hezbollah positions in the vicinity of Damascus, did not intercept the Turkish air force, which shot down the Syrian regime’s Russian-built Sukhoi Su-24 jet fighters, or Turkish drones that targeted the regime’s armored vehicles.
From his side, Turkey’s President Recep Tayyip Erdogan has announced his intention to travel to Moscow for a meeting with Russian counterpart Vladimir Putin, whose spokesperson has said that Russia does not want to expand the war zone.
What has worried Erdogan is the move north by Iranian and Syrian forces, which suggests that, not satisfied with expelling armed factions and recovering the rest of northern Syria, they intend to invade Turkish territory. Ankara has, thus, responded to the perceived threat by reiterating its obligation to defend its borders and citizens.
As for why Damascus and Tehran seem to want to expand the conflict zone northwards and, perhaps, invade southern Turkey, is based on the same justification Turkey gave for its invasion of the Syrian north last year; i.e. to establish a “safe zone” inside the Syrian territories, under the pretext of preventing the Kurds from attacking Turkey. The Damascus regime’s and Iranian forces might then decide to cross the border on the pretext of pushing armed groups, including Syrian and foreign fighters, out of Syria; thereby weakening Turkey and getting rid of millions of Syrians who oppose the regime.
Erdogan is now paying the price of his delay in military intervention, and for getting closer to the Iranians and Russians at the expense of the Syrian opposition.