At the very least Arab nations need to get involved because it's their fellow innocent Arabs (regardless of their religion) being victimized right now and they need to step up to ISIS.
There are two dynamics at play here - the never-ending struggle for political power, and the possibly more entrenched struggle for the identity of Islam. The second motivator has been the source of Arab on Arab violence since 632 AD, when the death of Muhammad left a power vacuum at the the head of the first Islamic caliphate - and not coincidentally the origin of the main division in Islam, Sunni and Shia.
To really appreciate the problem here it helps to keep in mind that for those of the more fundamentalist perspective, anyone belonging to a different version of Islam is fair game for murder, and those who do not believe in Islam are less than human and therefore killing them is akin to slaughtering livestock..
If you imagine that these folks caught up in this antiquated magical thinking can or will reason their way to any sort of concern for their fellow Arabs, then you haven't been paying attention - Bosnia, Kyrgyzstan, Iraq, Pakistan, Iran, Somalia, Ethiopia, Nigeria, Cote d’Ivoire, Cyprus, East Timor, Indonesia, Macedonia, Sri Lanka, Philippines....the willingness to slaughter each other by the tens of thousands is common, respect for each other and differing beliefs is not.
It is estimated that 90% of the violent conflicts around the world are motivated by Islamic theology, and that number is rising.
All this is not to say that all Muslims are violent, that is obviously not true - but it is a pretty clear indicator that a quite large number of them see Chapters 8 & 9 as a clear justification for violence against anyone and everyone they disagree with - specifically they interpret the concept of Jihad in the military sense, and place little or no value on the lives of anyone who does not follow their preferred interpretation of the Qur'an.
I would recommend to anyone wishing to better understand this conflict to read the Qur'an, to read first hand the instructions for when violence is justified, in the home, in the mosque, in the public square - with close attention to how anyone who isn't Muslim is referred to, and how those who deviate from Islamic teaching are to be dealt with - it will provide a much needed context to understanding the nature of this violence.