Often different Salafi armed groups focus on a perceived sectarian identity of their enemy, however absurd the construal of this identity may be. Regardless, why would many of these armed groups identify their struggles in this sense? I believe this is partly due to an uncritical application of what is largely medieval Islamic juristic tradition to to all contexts and times. For example, medieval Muslim jurists defined ‘Jihad’ as ‘qital al-kufar’ i.e. specifically to fight the disbelievers. There are other types of combat, that include Muslims (e.g. to fight rebels or bughat that revolt against a Muslim authority) but this is strictly, according to jurists, not a form of ‘Jihad’. ISIL, for example, label Abu-Muhammed al-Jolani (head of Jabhat al-Nusra) as a sinner and ‘baghi’ or a rebel against what they view as their legitimate Islamic authority.
Jihad, by medieval jurists, was then differentiated to include defensive and offensive warfare, with any offensive war requiring the sanction of a Muslim ruler. However, the legitimacy of an offensive war has been challenged by contemporary Muslim scholars e.g. Muhammad al-Ghazali, Muhammad Sa’id Ramadhan al-Bouti, Wahbat al-Zuhayli and many more. The opinion that ‘Jihad’ is restricted to a defensive military struggle to defend the Muslim community or life and property is now the given orthodoxy (Salafi scholars still, by far, reject this opinion).
Thus to justify any military combat as a ‘Jihad’, Salafi groups will seek to ‘other’ their enemies along strictly religious categories, even if these categories are absurd and make no sense even to their enemies. Following from this, Jabhat al-Nusra, ISIL and others state their enemies as Zoroastrians, Nusayris, Rafidha and ‘secular’ apostates etc. There is also demonisation of their enemy as they are on the wrong end of a cosmic struggle and all of them are destined for eternal damnation and they, on the other hand, are the group of righteous believers foretold in scripture carrying the banner of ‘Jihad’ to the end times.