After Iraq, Iran, and Turkey defeated ISIS in 2017, they invaded Iraqi Kurdistan. This move enabled Turkish forces to expand militarily and establish many bases within Iraqi borders.

With Assad gone, Syria's Kurdish government has an uncertain future. 

The SDF in Northern Syria have built their house on sand. Many pro-FSA Arabs live in the northeast, and much of the SDF itself (2nd column from the right) is composed of such fifth column elements. A joint Syrian-Turkish invasion would likely be accepted as a liberation war.

US & Israeli officials are worried about defending a land corridor in Syria to prevent regional actors such as Turkey, Iran, and various Islamist factions from posing a threat to Israel.

Such a corridor would interfere with Turkey's strategic goals in Syria, especially just after an exhaustingly long civil war and newly found Turkish political dominance in the country. It is unlikely that Turkey would let this opportunity pass them by.

Meanwhile, Israel is perhaps over-extending itself during a lengthy multi-front war, as US-competitors Iran & Russia seem to remain steadfast after trading Assad for the new government in Syria established by the FSA.

Since Israel is conquering land over claims from thousands of years ago, does it not set precedent for Turkey to project Syrian sovereignty over Ottoman-era boundaries? Both armies are on the move now, and Assad is no longer in between them. What happens next? Enter Trump:

Situated in Golan Heights, the aptly named Trump Heights settlement symbolizes the intense involvement that the next Trump administration will have in the region. Rather than pivoting US strategic positioning to East Asia, Trump will have his hands full with Syria and Israel.

Dealing with Syria for Trump means dealing with Turkey. Many of Trump's allies have a very CENTCOM-centric focus on foreign policy. Keeping Neocons out of his admin is crucial in preventing the US from being bogged down in a forever war fueled by ancient blood grievances.

The factions that overthrew Assad in Syria are not unipolar either. Jolani's HTS is gaining distance from Turkey relative to the SNA by playing good cop with the SDF. The Southern Front & SFA are more secular and aligned with US/Israel forces.

Turkey will have to stabilize Syria first and may have to begrudgingly accept HTS primacy among other factions, along with supporting Jolani's legitimacy. Thereby choosing friendship with the HTS rather than completely losing them over failed attempts to control his territory.

Lastly, some have theorized that Israel and Turkey agreed to partition Syria. Something akin to the Molotov–Ribbentrop Pact and the ramifications it had for Poland. 

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Sources: Analysts - CGI - News Agency