Depending on which right-wing lunatic you speak to, the US is under numerous existential threats. Well, I'd like to offer you a centrist's existential threat!
The end of the Cold War left the paranoid nothing to be truly paranoid about. Fortunately, bin Laden popped up and gave them an even better thing to be scared of. In the subsequent years, its become a whos who of ethereal, scary threats to the US way of life. They are all people or states. What about currencies?
What about the evil, Godless Euro?
To the American mind, Al-Qaeda is still probably the top scary shadowy threat. No-one knows who they are (they could be your neighbour, if they are swarthy looking enough!) or when they will next strike!
Iraq, being a state, was a far easier to understand and identify target. So they became the existential threat of the week. That Iraq was a toothless tiger due to the Iran/Iraq war, the first Gulf war and a decade of crippling sanctions didn't really matter. Let alone the fact that the swathes of WMDs couldn't be found depite that Iraq had become the most monitored state in the history of the world.
A few years ago, Iraq was an existential threat. North Korea looked like holding the title for a while, but since it possile really
could have been an existential threat with nukes, it has moved into the too hard basket.
Today, it looks like Iran is the bad guy.
Purely coincidently, Iraq & Iran both have large oil reserves. Of course, this has nothing to do with them being existential threats, unless its an existential threat to the SUV.
One existential threat, that is more real than those listed above is that of the Euro.
The US dollar is a defacto common unit. Any currency exchange is not bilateral, but in fact trilateral. For example, a Australian dollar trade with Japanese Yen does not happen directly. Technically, both currencies go via the US dollar. Until the Euro, the only modern accepted way to measure a currency was against the USD, which was always 1. (It does actually fluctuate, but this is reflected in other currencies). The concept isn't new. Previously, the Pound Sterling was considered a base currency.
In order to trade internationally, a state must hold in USD the equivalent of its own currency in circulation. Of course, this USD reserve is a significant investment of which the value must be preserved. So imagine if you will, that the rest of the trading globe has a massive amount of USD which represents its own currency's value. Oil is only traded in USD, and the value is labelled 'Petrodollars'.
Simply put, Petrodollars aren't a real currency as such, but the value of oil versus the defacto common currency. OPEC states trade oil for USD and only USD, and oil is valued against the USD. One could even go as far to say that the petrodollar is the lowest common denominator for the industrial world.: The base commodity vs. the base currency of industry. Once again, every state that wishes the lubrication of industry to remain affordable, must maintain the value of it's USD reserves.
The effects of thes two factors mean every state has a massive vested interest in maintaining the value of the USD. It has the effect of being a global safety net which holds up the entire US. On it's own, the US economy isn't strong enough to maintain its standard of living.
The Euro is a currency that holds it value based on a aggregated value of the economies of the states that use it. Some, like Germany are economic powerhouses and others are near basketcases. One difference is that the Euro is also growing. States are being added. (Turkey, the only muslim democracy, is the next state being reviewed) The Euro can effectively compete against the USD as a common currency. Having a alternative common currency would be simply disasterous for the US in particular, and the world in general.
What would happen if OPEC converted over to the Euro?
Overnight, OPEC states would earn billions through arbitrage, the difference in values between the USD and the Euro. The demand for the USD would shrink significantly, sending its value down, down down.
This may trigger a sell-off from other states to dump their declining US reserves and buy Euros. This would have a 'snowball' effect. The globe would be awash with near valueless USD. The Euro would rise, making further profits for OPEC states and making oil significantly more expensive. The recent rises are simply tasters. The entire industrialised globe would enter a depression. In the short term, much of the US economy would simply crash. It would be many years before the value of the US economy would actually be able to hold up the currency on its own. Of course, it would only then be in parity with the US economy. It will have nothing like the power of the current USD.
How does this relate to the Bush adventures in the middle east?
Bush has publicly stated that "The American way of life is not negotiable" in 2001. The Iraq war would probably stand up as a very good example of what the US is willing to do to maintain it.
Saddam Hussein, in 2002 had converted his petrodollars to the Euro. Iraq literally made billions overnight. The invasion occurred soon after, and Iraq's petrodollars were soon switched back to USD. We all know how much of a mess Iraq is today. Iran too, is looking at, or in the process(depends on where I read) on converting to a Petroeuro.
Iran issue is more complicated. Iran is a stronger, more stable economy. Cultrually, it is more coherent than the arbitrary collection of peoples Iraq ever was. It is also a significant OPEC member. Iran is in the process of setting up it's own bourse; an exchange for oil trading. Technically, Iran is holding a couple of cards. It has the ability to restrict flow of oil, sending up the price today. It can also convert to Euros and reduce the USD's value, and possibly trigger a mass conversion by OPEC.
Iran obtaining nuclear power is simply a case of buying protection. The US is loath to attack a nuclear state. It is about the only equaliser Iran has from military intervention.
Overall, we can forget about WMDs, we can forget about terrorists blowing themselves up. We can forget about terrible muslims coming to rape our daughters. They are threats that are easily tangible to even the most fundamental southern baptist, and easily fought off. However, Global economics and the threat of the Euro to USD hegemony are an even more shadowy threat than Al-Qaeda.
And it could really blow up all World Trade Centres.