If we had operated that way during WW2, it would be like quitting and declaring an armistice after the Battle of the Bulge, letting Hitler remain in power under the belief that he has been "contained."
Historian checking in! Gotta throw a flag here for some clarification. It is important.
ISIS represents an ideology or a very abstract band of militants, at best. Hitler, on the other hand, represented a nation. A nation has a system of government, a populace, an army, an economy, assets, foreign policy, advisors, etc etc etc. Isis does not have these things. To compare fighting a nation that has declared traditional war to the struggle against ISIS is not a good one. ISIS does not have to answer to anything outside of their own circle. Germany did. They had to balance and maintain things that ISIS does not. Germany operated under what we generally like to call rules of war. (To be clear: this is not including the Holocaust, this is discussing formal war as a nation and why comparing the two is not always accurate.) ISIS does not operate under these rules and their tactics are much more difficult to predict because they don't have an "army" or "generals" or "presidents/chancellors, etc". There is no diplomacy, no lines of communication, no representatives, nothing, nada, zip.
Summary: It is much easier to fight a nation. You can defeat a
nation. It is much harder to defeat an
ideology.
For these reasons (and a few more if I wanted to dedicate more time to it), the comparison between the two is a faulty one.