I think this will only stop when everything comes under ISIS in Iraq. Only then it will be affordable for US or NATO to be at War with ISIS. Even Russia will be eying the opportunity to let its army go into the war.
That will be a horrible strategy against the ISIS. Imagine what would happen if they conquer the whole of Iraq and Syria. All the minorities who are living there (Yazidis, Kurds, Assyrians, Mandeans.etc) will be exterminated. All the Shiite shrines will be destroyed, along with the other non-Muslim places of worship. And the ISIS will be having a potential recruitment pool of some 50 million people, which will make them invincible against a normal ground offensive. IMO, the only chance to defeat the ISIS is to attack them right NOW.