At Counterpunch, Michael Hudson has penned an important article that outlines the important connections between US foreign policy, oil, and the US dollar.
In short US foreign policy is geared very much toward controlling oil resources as part of a larger strategy to prop up the US dollar. Hudson writes:
The assassination was intended to escalate America’s presence in Iraq to keep control of the region’s oil reserves, and to back Saudi Arabia’s Wahabi troops (Isis, Al Quaeda in Iraq, Al Nusra and other divisions of what are actually America’s foreign legion) to support U.S. control of Near Eastern oil as a buttress of the U.S. dollar. That remains the key to understanding this policy, and why it is in the process of escalating, not dying down.