The governing apparatus of many regional power structures - in particular the House of Saud who rule Saudi Arabia - is dependent almost entirely on revenues from oil. With much of the wealth of the world stemming from cheap energy provided by oil, the most prosperous nations on earth have become increasingly enmeshed with regional political matters.
Even Jimmy Carter - who can hardly be considered to be among the first rank of belligerence when it comes to US leaders - made the importance of the region clear in his 1980 State of the Union Address, telling Americans that:
"An attempt by any outside force to gain control of the Persian Gulf region will be regarded as an assault on the vital interests of the United States of America, and such an assault will be repelled by any means necessary, including military force."
This is a neat summation of American - and by extension Western - interest in the region. The oil that flows from the ground may belong to those who rule the area, but those rulers can only expect to survive on the back of American support and power.
We needn't discuss the tangled web of history here, but this geopolitical significance is the reason for the presence of American troops in Saudi Arabia. Indeed, it was this US presence that bore the terrible fruit in the emergence of Al Qaeda. Osama bin Laden was, in part, motivated by the desire to rid his country of American military forces and thus enable the overthrow of the House of Saud. From the wellspring flowed a spring of violence that continues to lap around the feet of the world to this day.
Against such a complex background it is little wonder that conspiracists postulate that the Iraq War had nothing to do with the so-called "War on Terror" but was actually a war for control of resources. In this reading of history, the 9/11 attacks on America made the US power structures wake up to the prospect of losing their stranglehold on the Middle East.
This in turn necessitated making direct military interventions in the region to ensure the installation of 'friendly' regimes who would continue to provide the cheap oil on which the US economy was and is dependent.
Using the flimsy - and false - pretext of an Al Qaeda presence in Iraq, the US (and, most pertinently to us) and UK launched an invasion of Iraq in order to secure oil supplies and even more cynically to award contracts to major corporations such as Halliburton and Blackwater.