The primary motive for Western intervention in the Middle East region is always access to oil and gas supplies, particularly for European countries as a counter balance to Russia being the dominant energy supplier, otherwise they would not give a damn who runs the show as long as the oil keeps flowing, and it is not the chief reason the war has dragged on so long. There is also a regional power struggle involving Iran, Saudi Arabia, Israel and Turkey who see the disintegration as an opportunity to seize control of more territory and resources. Long term goal is get the oil and gas flowing to Europe, otherwise why is NATO involved?
Israel has been consolidating it’s hold on the Golan and running bombing raids against the Assad regime to further it’s interests as well as backing the Kurds. Per the Yinon plan Israel hopes to create a patchwork of weak and divided states in the region that they can play against the other. (divide and conquer).
The United Status is backing the creation of Kurdistan as it’s puppet in the region and has been involved in the coup against Turkey. It is also allied with Saudi Arabia and Israel and commands the NATO presence in the region. The United States also has it’s Government military industrial complex with their iron rice bowls. They also nominally control a puppet government in Iraq and Jordan.
The Turks are trying to extend it’s control down to Mosul in Iraq (oil) and the power regime has been benefiting from the oil smuggled out of the region (shipped to Israel), in addition it needs to stop the development of an independent Kurdistan or at least have it’s own puppets in change.
Russia is primarily a resource based economy and has it’s own arms industry so their interests are also tied up with oil and gas and the need to secure their southern borders in the Caucasus (and oil pipelines) and not have a constant safe zone for their attackers to retreat to and attack them from. Russia is also part of the Shanghai Cooperation Organisation as is Iran nominally.
Saudi Arabia wants to prevent the development of the Shia crescent and exercise control over the region and it’s oil and is currently pulverising Yemen with weapons supplied by the United States (the oil for weapons trade). Iran is providing some backing for the Houthis who themselves have evolved to counter the spread of Wahhabism.
Qatar is on the wrong side of the Arabian peninsula and needs to get it’s gas to market, shipping gas by boat is expensive.
Then there is Syria whose borders were defined by the Anglo-French Sykes Picot agreement in the aftermath of the defeat of the Ottoman empire (modern day Turkey) and is really a composite of different tribes, ethnicities and religions going back thousands of years, the internal fighting should have mostly burned itself out within two years , but it keeps getting fed from outside.
Iraq is now in the Iranian sphere of influence as is Afghanistan, both of which countries have American and NATO troops stationed in them.
ISIS is a loose canon made up of disaffected Sunni Tribes in the wake of the American conquest of Iraq, it plays off the US empire in a bid to carve out it’s own territory in the region. NATO and the US hope to confine the ideology to the desert. Saudi Arabia hopes to use it a a counter balance to the Shias and also to secure the oil in the area (under the guise of a peace keeping force.)
The Egyptian regime is propped up by Saudi Money, that regime are mostly concerned with the insurrection in the Sinai with it’s oil and gas resources. Egypt has an uneasy alliance with Israel.