That's the most rational theory for oil, because all others simply do not make sense. No oil company is going to invest a cent in Iraq for as long as the Americans are there, because any contract will be renegotiated with whoever will capture power once they're gone - and because it won't be safe until they're gone. In the long run, we're all dead. John Maynard Keynes
In other words, if soft political control of oil producers is not possible, the US would move to direct political pressure and, failing that, military control, but populer resuistance and the fragility of oil infrastructure would result in not being able to gain control of the resources anyway.
But if the goal is not so much to gain control of more oil but to deny access to others, then the Iraq war is not so much of a failure.
What it is is a criminal scorched-earth approach to managing the global economy and resources. tens of millions of people stand to see their lives ruined because the bureaucrats at the ECB don't understand introductory economics -- Dean Baker