It’s about the money.
The announcement that the Iranian government will convert its foreign dollar holdings to euros might be the first step down the slope that results in oil sold internationally in euros. In isolation, the announcement is not major, as oil is still sold through the New York or London bourses in US dollars, therefore, the Iranian government will be converting payments received directly into euros.
The implied threat, however, and one that Washington definitely is taking seriously, is that Iran may try to introduce a third international oil bourse, one that operates in euros. Such a move would threaten the strength of the US dollar at a time when the US national debt is at historic (histrionic?) levels and could have serious economic implications. I’ve discussed some of the reasons why this could be so here, and I believe that the US is more worried about the stability of the value of the dollar than they are concerned with regional stability in the Middle East. The two are linked, but they are not in lock-step.
The oil is important because it gives the Iranians economic independence and leverage. The nukes are important because it puts an exlamation point on every statement everyone makes about the place. However, the power that oil has over the value of the US dollar, and the number of countries that might want to buy and sell it using euros, is the real clincher.
I think it is guarenteed that we will see the tension between the West and Iran ratchet up in the coming days and weeks as a result of this announcement.