You guessed it - natural gas, building a pipeline, thwarting Iran and Russia, and maintaining US hegemony in the region.
Here is a comprehensive analysis of the situation by Robert F. Kennedy, Jr.:
Secret cables and reports by the U.S., Saudi and Israeli intelligence agencies indicate that the moment Assad rejected the Qatari pipeline, military and intelligence planners quickly arrived at the consensus that fomenting a Sunni uprising in Syria to overthrow the uncooperative Bashar Assad was a feasible path to achieving the shared objective of completing the Qatar/Turkey gas link. In 2009, according to WikiLeaks, soon after Bashar Assad rejected the Qatar pipeline, the CIA began funding opposition groups in Syria. It is important to note that this was well before the Arab Spring-engendered uprising against Assad.
You can read the rest @
Sounds just like what the US did in Afghanistan, no?
And note well that Kennedy provides compelling evidence the US was indeed responsible for the rise of ISIS.
Once again, millions have to suffer and die so that Israel can thrive and a few oilmen can be rich. Why is it that We The People never seem to figure this out?