The northern Syrian region of Afrin has witnessed Turkish, Syrian and Kurdish military forces due to a diverse set of strategic interests.
And various contradictions among the different forces on the ground have arguably transformed the war from a fight between Syrian President Bashar Al Assad and rebels who want to overthrow him into a deeper conflict.
The Assad regime's goal is clear: restore government rule nationwide by the retaking of all Syrian territory.
Turkey, a NATO ally of the United States, was initially one of the biggest supporters of anti-Assad rebels. But in Afrin, a majority Kurdish region, it has shifted its main focus to driving out members of the People's Protection Units (YPG) away from its borders. Turkey sees the YPG as an offshoot of the PKK, a group of Turkish Kurds that has waged a three-decade insurgency against Ankara, initially seeking independence but now demanding autonomy.
However, the YPG and a broader Arab-Kurdish coalition known as the Syrian Democratic Forces (SDF) have won popular support from the West as being the most effective ground force in the battle against ISIL insurgents. Above all, the United States has backed the YPG with military support that is now in the arsenal being used against Turkish forces.
Last month, Turkey launched an air and ground offensive on Afrin, prompting Mr Al Assad to denounce the operation as a "blatant attack" on Syrian sovereignty.
At the request of the region's Kurds, however, Mr Al Assad directed pro-governmental militias, to "support the locals against aggression waged by the Turkish regime."
Upon entering Afrin on Tuesday evening, militias came under shelling from Turkish forces, who said they had fired "warning shots" at the "pro-regime terrorist groups".
Pro-government forces and Kurdish-led fighters have fought each other elsewhere in Syria, and Damascus opposes the Kurds’ demands for autonomy. But in Afrin they have a common enemy: Turkey.
"Groups aligned to the Syrian army came to Afrin, but not in the quantity or capacity to stop the Turkish occupation," YPG spokesman Nouri Mahmoud said.
The militias though could curtail Turkey's advance in the Afrin - the city has not yet been taken but Turkish President Recep Tayyip Erdogan has said his forces will - but it also creates the potential for more fighting and military miscalculation.
"The Syrian army must fulfil its duty... to protect Syria's borders,"” Mr Mahmoud said of the potential for major battles.
And Turkey has warned Mr Al Assad of "serious consequences" if his troops enter Afrin to help the YPG.
Kurdish forces, stuck in the middle between Turkey and Syria's army, want to claim their autonomy in the north, where they have set up ruling councils and held elections. They seek to prevent Ankara and Damascus from attacking their territory.
The complexities are underpinned by Mr Al Assad and the YPG both regarding Turkey as an enemy: Ankara was one of the biggest powers supporting the anti-Assad rebels early in the war.
Despite international calls to halt the Afrin operation, Turkey has said its forces could extend their offensive as far as Manjib in Syria's east. Doing so could take them perilously close to US forces, who are there to maintain an effort against a possible ISIL resurgence.