How ISIS obtained its arms

"Then there’s the related question of how ISIS has become so well-armed and powerful. There are many causes, but a leading one is the role played by the U.S. and its “allies in the region” (i.e., Gulf tyrannies) in arming them, unwittingly or (in the case of its “allies in the region”) otherwise, by dumping weapons and money into the region with little regard to where they go (even U.S. officials openly acknowledge that their own allies have funded ISIS). But the U.S.’s own once-secret documents strongly suggest U.S. complicity as well," (thanks Amir)