Response to the question of why the US address such military mission? The most reasonable ideas would be that the US addressing of Military International Relation Affairs: The Syrian government had been in suffering for years from the groups of opposition as well as the group of ISIS. The opposition is alliance of US and Western World while the ISIS showing their killing machine across international media and foreign eyes communities without US military intervention. The military public affairs and the Psychology department can explain to local communities or local media of reason to down the non-democracy of Syria government but may not easily to cope with the International media agencies or social media atmosphere. Thus, the mission to " advise and assist" to opposition against ISIS/ISIL would be a step to INTERNATIONAL RELATION platform.
As we can see the below list, it is a balance force among the Syria government, ISIS and opposition forces. Russia is a backbone of Syria government while the US is central force for opposition. Russia, recently had been demonstrating their military power tools in attacking the ISIS. Today, the US also test its military hypothesis in advising and assisting to opposition in counter the ISIS as well as Russia doing.
|The Syria Government supports (NPF) by|
|The Opposition supports by|
Ajnad al-Sham Islamic Union
Army of Mujahedeen
Syrian Turkmen Brigades
Jabhat Ansar al-Din
ISIL supports by
Yarmouk Martyrs Brigade
Rojava support by
Iraqi Kurdistan Iraqi Kurdistan