While Ramadi has been retaken in Iraq, in no sense has ISIS been fully defeated. That war will continue at least through 2016, and very likely beyond.
This story in the Atlantic ran back in March and is a bit dated, but what it says about the religious "thinking" behind ISIS remains relevant. Especially:
. . .much of what the group does looks nonsensical except in light of a sincere, carefully considered commitment to returning civilization to a seventh-century legal environment, and ultimately to bringing about the apocalypse.That's a recipe not only for fanaticism, but persistence.
Some caveats about the article: They ARE psychopaths, and the territorial gains were only possible because of the specific political conditions in both Syria and Iraq. Nor should "mere" political power be underestimated as a motivator.
And contrary to the article's conclusion, direct, violent, consistent confrontation is the only way to deal with the movement. Unfortunately, it's likely that, once ISIS is defeated, other somewhat similar "movements" will spring up until Islam's civil war runs its course.
One of the biggest problems in understanding what's going on is our understanding of our own history. We've been taught to think of war in terms of the 20th century Western wares, World War II especially. Even Vietnam does not supply the kind of metaphors or framework that truly apply here. And thinking long term while fighting short term is not something most humans are good at.