At the root this is about power and establishing the caliphate. Some aspects could be about the price of oil and who benefits from controlling the supply. The real objective is dominance over an empire. Turkey, Syria, Iraq, I ran, Jordan, SA, Eygpt, Libya, Israel, (all the other little countries). Erdogan has made public statements that he is the caliph.
October 2014 US Vice President Joe Biden told a Harvard gathering that Erdoğan’s regime was backing ISIS with “hundreds of millions of dollars and thousands of tons of weapons…” Biden later apologized clearly for tactical reasons to get Erdoğan’s permission to use Turkey’s Incirlik Air Base for airstrikes against ISIS in Syria, but the dimensions of Erdoğan’s backing for ISIS since revealed is far, far more than Biden hinted.
ISIS militants were trained by US, Israeli and now it emerges, by Turkish special forces at secret bases in Konya Province inside the Turkish border to Syria, over the past three years. Erdoğan’s involvement in ISIS goes much deeper. At a time when Washington, Saudi Arabia and even Qatar appear to have cut off their support for ISIS, they remaining amazingly durable. The reason appears to be the scale of the backing from Erdoğan and his fellow neo-Ottoman Sunni Islam Prime Minister, Ahmet Davutoğlu.