Bombing did not stop the Viet Cong, partly because they dug a lattice of tunnels. This lesson has been learned by everyone and his cousin since, and The Black Daesh are naturally doing the same thing to escape these sore fires from heaven. They choose a nice house in the suburbs, and dig down. See the tunnels on YouTube under their areas of occupation in Sinjar, the suburbs of Damascus etc. As someone pointed out earlier, the bombs continue to smash infrastructure on the surface. Will what we do be more than symbolic?