So argues Adil Ahmad Haque in his article on Newsweek:
In plain terms, the U.S. may have a legal right to protect non-state partner forces who are exclusively “conducting legitimate counter-ISIS operations,” but has no legal right to protect non-state partner forces who are pursuing regime change or other political objectives.
There is no right of collective self-defense of non-state actors, and the right of collective self-defense of other states only justifies measures that are necessary and proportionate means of achieving legitimate defensive aims.
For this reason, among others, the mixed motives of the U.S.-led coalition and its non-state partners compromise the legal basis of their military operations and draw them into conflict with Russia—both legally and militarily.
Read the whole piece here.