Qatar: F-15 deal done, what made this happen?

signed on 14/6/17 at the Pentagon a deal for 36 fighter jets of type F-15QA in favor of the Qatari Air Force (QAF). Mattis is said to have played a major role in getting the deal done at this stage. Tactical Report has prepared 541-word report to shed light on the subject and tell what made the deal go through, technically and politically.