Edited version of original here:
http://jwaversyria.blogspot.com/2018/01/turkish-invasion-into-kurdish-afrin.html
On the 21st of January this year, Turkey launched the long-anticipated operation into the northwestern Syrian province of Afrin, a small part of the large territory held by the Syrian Kurds. But this operation is just the beginning of larger scaled operations in northern Syria by the Turkish military.
The Syrian Kurds greatly threaten President Erdogan's hold over Turkey to such an extent that, with the entry of Russia into the Syrian war, President Erdogan has been forced into recalculating his regional policy. Though publicly denouncing Bashar Al-Assad and demanding his removal from office, privately, Turkish opposition to Assad has softened considerably.
https://sputniknews.com/politics/201701281050105764-turkey-syria-russia-iran/
It is US policy, not Russian policy, that threatens Turkish interest in the region, and that because the US is funding the Syrian Kurds after the destruction of ISIS in Syria. Though Bashar Al-Assad is secular and not Islamist, he leads the Syrian Arab Republic, which favours the Arabs over the Kurds. But the US-supported Syrian Democratic Forces are largely Kurdish, and many of these fighters are allied to the YPG, which has been waging war against the Turkish government for decades.
Sentiment in Turkey is perhaps best expressed by MP Metin Kulunk: "Syria will become a second Vietnam for the US." This sentiment will likely embolden President Erdogan into not stopping the Turkish invasion into Afrin, but additionally fighting for control of Manbij to force the Kurds to the eastern side of the Euphrates River.
https://sputniknews.com/middleeast/201711161059157430-syria-second-vietnam-for-us/
Turkish ambition may not be limited to west of the Euphrates, either. Russia, Syria and Iran are not interested in seeing a long-term US presence in northeastern Syria. They see that this undermines the territorial sovereignty of Syria, but any attacks on the northeastern enclave by Russia, Syria or Iran would ignite serious hostility from the US.
Turkey, on the other hand, is a NATO ally. Turkish war on the US-backed Kurds in Syria would have more serious consequences for the US than anyone else. In such a scenario, the US would be forced to use Iraq for transit or withdraw entirely from Syria. Turkey would become a more permanent member of the Russian axis in the Middle-East, would purchase the Russia-designed S-300 missile defense system and result in Turkey's expulsion from the NATO alliance.
Either the US would abandon the Syrian Kurds and make an exit strategy from Syria, which is a shared goal of Russia, Syria, Iran and Turkey - or the United States would be forced into a conflict deeply unpopular at home.
As the Turks seek to remove the US-Kurdish presence from Syria, this might give Russia, Syria and Iran the green light they need from Turkey to cede the rebel-held province of Idlib to the Syrian government. Idlib is largely under the control of Al-Qaeda, but has also served as a dumping ground for rebels from other regions in Syria.
War between Turkey and the United States for northern Syria would humiliate the US and cede the region to Turkish influence - in exchange, Bashar Al-Assad would regain control of Idlib province. Such an arrangement would mean no further roadblocks would exist for Turkey, Russia, Syria and Iran to seriously negotiate a political settlement for ending the Syrian civil war.
