the group has been around over a decade ago and involved in the Syrian civil war for a coupel of years; the west/arabs funded funded other groups in Syria which have either since joined or been defeated by Isis; the claimed army of 30k is estimation, others vary from a mere 4000 to 50000; the...
of course they will. we've seen how peacefully passive they've been with the iraqi christians, shia and other local religious sects they've found inhabitating the lands of Iraq and Syria. they let them join them, thats how nice they are.