Oops posted to soon, meant to quite the last two paragraphs in particular - suggesting world leaders find it politically inconvenient to put any pressure on Turkey, even though this would be the most effective way to tackle ISIS - elsewhere in the article it is hinted that world leaders find other less effective ways to "wage war" on ISIS, such as boarder controls and restricting immigration, more politically expedient... :
"Had Turkey placed the same kind of absolute blockade on Isis territories as they did on Kurdish-held parts of Syria, let alone shown the same sort of “benign neglect” towards the PKK and YPG that they have been offering to Isis, that blood-stained “caliphate” would long since have collapsed – and arguably, the Paris attacks may never have happened. And if Turkey were to do the same today, Isis would probably collapse in a matter of months. Yet, has a single western leader called on Erdoğan to do this?
The next time you hear one of those politicians declaring the need to crack down on civil liberties or immigrant rights because of the need for absolute “war” against terrorism bear all this in mind. Their resolve is exactly as “absolute” as it is politically convenient. Turkey, after all, is a “strategic ally”. So after their declaration, they are likely to head off to share a friendly cup of tea with the very man who makes it possible for Isis to continue to exist."