In 2000 Iraq made moves to create a new trading market, except the trading currency would be Euros, not US dollars. This seriously threatened the US economy and so moves were made to remove Saddam and at the same time remove the Euro oil trading scheme. Two birds with one stone if you like. And this is why the US won't leave Iraq anytime soon, because the oil reserves are too important.
Now since about 2005 Iran has been trying to finish what Iraq never could, ie the Euro oil trading scheme. This has again seriously threatened the US power regime, and hence why noises are being made about military action being taken against Iran. It has nothing to do with Iran's nuclear capability, and everything to do with oil.
The Iranians are about to commit an "offense" far greater than Saddam Hussein's conversion to the euro of Iraq’s oil exports in the fall of 2000. Numerous articles have revealed Pentagon planning for operations against Iran as early as 2005. While the publicly stated reasons will be over Iran's nuclear ambitions, there are unspoken macroeconomic drivers explaining the Real Reasons regarding the 2nd stage of petrodollar warfare - Iran's upcoming euro-based oil Bourse.
In 2005-2006, The Tehran government has a developed a plan to begin competing with New York's NYMEX and London's IPE with respect to international oil trades - using a euro-denominated international oil-trading mechanism. This means that without some form of US intervention, the euro is going to establish a firm foothold in the international oil trade. Given U.S. debt levels and the stated neoconservative project for U.S. global domination, Tehran's objective constitutes an obvious encroachment on U.S. dollar supremacy in the international oil market
http://www.globalresearch.ca/articles/CLA410A.html
Could the proposed Iranian oil bourse (IOB) become the catalyst for a significant blow to the influential position the US dollar enjoys? Manifold supply fears have driven the price of crude oil to its recent high of US$67.10 - only a notch below its highest price in inflation-adjusted dollar terms. With the world facing a daily bill of roughly $5.5 billion for crude oil at current price levels, it becomes apparent that sellers and purchasers of the black gold are looking into all ways that could lead to a financial improvement on their respective sides.
http://www.atimes.com/atimes/Global_Economy/GH26Dj01.html
Contemporary warfare has traditionally involved underlying conflicts regarding economics and resources. Today these intertwined conflicts also involve international currencies, and thus increased complexity. Current geopolitical tensions between the United States and Iran extend beyond the publicly stated concerns regarding Irans nuclear intentions, and likely include a proposed Iranian petroeuro system for oil trade.
Similar to the Iraq war, military operations against Iran relate to the macroeconomics of petrodollar recycling and the unpublicized but real challenge to U.S. dollar supremacy from the euro as an alternative oil transaction currency.
http://www.energybulletin.net/7707.html