The Obama Administration has been funding and training ISIS or ISIL for more than 3 years to overthrow the Syrian central government. ISIS has been supplied with weapons and money to carry out the attacks on Syria.
Also part of Obama’s plan was to get rid of the central government in Iraq and break it into 3 parts Shia, Sunni, and the Kurdish area but when ISIS started to close in into the western controlled areas they had to take action. The U.S. started bombing ISIS militants to push them out of western controlled areas. That is basically the U.S. saying you can’t touch these infrastructures because that is not what they agreed to and because those oil fields are owned by the US and its allies.