Although Isis militants initially succeeded in 2014 with the U.S. weapons, they took from Iraqi army in Mosul, but after that Isis took weapons from all the sides like Syrian rebels, Shia militias, Kurd militias. They also used & using till now the U.S , Russian, Saudi , Iran, Syrian & even Chinese made weapons. So one could blame all global powers from either side who are giving the weapons to their own linked militias, which end up in ISIS hands.