As I often say, “It’s all about the oil. It’s always all about the oil.”
Turkey’s president Erdogan may protest that he and his country are not involved in illegal oil trade with ISIS (and as a consequence are also looking after ISIS interests and funding them), but Russia has provided proof that this trade is going on and is why they are making this a major part of their thrust in the war against ISIS.
This is of course why Turkey shot down the Russian military aircraft recently.
Image: The routes of alleged oil smuggling from Syria and Iraq to Turkey © syria.mil.ru