There are currently two wars being fought in northern Syria.
First is the war in Idlib province between the Bashar al-Assad dictatorship and various rebel groups. Assad's army, backed by Russian air power, is trying to recapture Idlib, which has been a centre of opposition to the regime since the upsurge of popular protest throughout Syria in 2011.
For several years after 2011, much of the province was controlled by rebel groups with democratic goals. But subsequently some of these groups were crushed by reactionary Islamist groups. Others were coopted by Turkey, which supplied arms to selected rebel groups if they agreed to become part of Turkey's war against the Rojava Revolution.
The strongest armed group in Idlib today is Hayat Tahrir al-Sham, a very reactionary group with a history of persecuting religious minorities. Thus the war in Idlib is now a conflict between what academic Gilbert Achcar calls "two counter-revolutionary poles".
The Assad regime has being making progress in recapturing Idlib. Hundreds of thousands of people have fled the fighting, in particular the bombing by Russian and Syrian air forces.
Turkey, which has had some troops stationed in Idlib since 2018 as a result of the deal with Russia, has sent more troops into the province, seemingly to deter further advances by Assad's troops. Thirteen Turkish troops have been killed in aerial and ground artillery bombardments by Assad's forces.
The second is the war of resistance being fought by the Syrian Democratic Forces (SDF) against the Turkish invasion and occupation of a large part of northern Syria. Turkey aims to crush the democratic revolution, which began with uprisings in three predominantly Kurdish areas, known collectively as Rojava, in July 2012. The revolution then began to spread to adjacent non-Kurdish areas, leading to the establishment of the Democratic Autonomous Administration (DAA) of northern and eastern Syria.
Turkish troops first entered Syria in August 2016. They moved into the town of Jarablus and adjacent areas with the aim of blocking further advances by the SDF, which had liberated large areas of northern Syria from the so-called Islamic State (ISIS).
In January 2018, Turkish troops accompanied by their Syrian proxies invaded Afrin, a predominantly Kurdish area. They captured Afrin, causing hundreds of thousands of people to flee. Guerrilla warfare against the occupiers continues.
In October 2019, Turkey and its proxies invaded a strip of Syrian land along the Turkish border between the towns of Ras al-Ain and Tal Abyad. They are trying to expand their area of control but are being resisted by the SDF. Once again, hundreds of thousands of people have had to flee their homes.
The Assad regime's attitude to the Turkish invasion of much of northern Syria has been contradictory. On one hand Assad sees the Turkish attacks as useful in weakening the SDF and undermining the DAA. He hopes this will force the DAA to accept the restoration of his regime's control over northern and eastern Syria.
On the other hand, Assad fears that Turkey will permanently occupy a large part of northern Syria. Hence, he has tried to put some limits on the extent of Turkey's invasion. There have been some clashes when Turkey has tried to expand its area of control beyond what the Assad regime had agreed to accept.
However, the main resistance to Turkey's invasion has come from the SDF, which also has to deal with terrorist attacks by ISIS.