People who work in the defence and security field frequently fall into the trap of assuming that all the actors in a particular situation will act in their own best interests. This is the essence of so-called realpolitik: the belief that a government or major non-state player seeks always to secure or improve its situation by diplomatic, economic or military means. And, as a general rule, this is probably a reasonable assumption.
Nevertheless, it is not a fixed law of nature. Some regimes do act in a manner that can only be described as irrational or self-harming. World history since, say, 1900, offers us several glaring examples.
In his notorious book Mein Kampf published in the 1920s, and in numerous speeches, Adolf Hitler rightly berated the German leadership of 1914-18 for involving the country in a war on two fronts, stretching its resources beyond breaking point. Yet in power, and having started the Second World War on his own initiative, Hitler then proceeded to make the same mistake by attacking the Soviet Union in 1941 before he had defeated the British. He devised all sorts of rationalisations to justify this decision, but the mistake is clear, and of course proven by the outcome.
Some modern regimes have similarly shown a cavalier disregard for reality in embarking on foolish military adventures. Saddam Hussein's 1991 invasion and (very temporary) annexation of Kuwait was one example, as was the same regime's defiance of the post 1991 sanctions and inspection system – the latter, of course, providing George W. Bush's administration with the perfect pretext for its own piece of needless adventurism, the disastrous 2003 invasion of Iraq, the costs of which have yet to be fully counted. If ever there was a lose-lose scenario for both sides, that was it: Saddam lost first his power and then his life, and the Americans squandered in the post 2003 Iraqi morass resources that could have made the difference in Afghanistan.
If you've been reading about recent threats from Iran to close the straits of Hormuz, their recent spate of showy military activity in the region and, most recent of all, their "advice and insistence" that a US aircraft carrier which left its base at Bahrain (inside the straits) should never return, don't to get too excited or alarmed.
On any rational assessment, the Iranian regime is incapable of closing the Hormuz Straits for more than a short period, and it is certainly incapable of preventing the movement of American warships in or out of the base at Bahrain. Should it attempt to do so, it will hand the US the best possible excuse for an overwhelming military response.
It would of course be both unnecessary and incredibly stupid to actually invade Iran. That would be a mistake that would make Iraq look like a picnic. But while Bush the Younger and most of his neo-conservative cronies were fools, the present administration appears to be much smarter and would, I'm sure, mount a far more judicious response to serious Iranian provocation. The destruction of Iranian sea and air power is something the United States, possibly supported by some of its allies, is well able to accomplish if Teheran provides sufficient reason for so drastic an action.
It pays to bear in mind that the present Iranian regime remains in power only because of a rigged electoral system manipulated by fundamentalist Shia Ayatollahs, and enforced by its armed thugs against massive popular discontent. It is, in short, by no means domestically secure. There are millions of Iranians who want this regime gone.
If it is foolish enough to seriously challenge US power in the ways it now threatens, it will be defeated, and defeated badly. It will suffer a massive loss of credibility and would in all probability face serious domestic security problems.
That does not mean, however, that a post-fundamentalist Iran would be a nice pro-western state. The nuclear program, for instance, has wide support in Iran, far beyond the present ruling clique. But a rational regime in Teheran would no doubt be prepared to negotiate the issue on a reasonable basis. If such an Iran desires civilian nuclear power, a halfway sensible west could accept this, with the appropriate safeguards employed by other states which use this technology. (I leave aside here the serious objections – mostly to do with safety and waste management – to nuclear fission power, though it's worth noting that as an earthquake-prone country Iran under any sane government needs to consider these issues itself.)
In the modern era, and excluding the issue of terrorism of the Al Qaeda variety, it is regimes which act irrationally which pose the greatest security threat. Because they are irrational, they are very difficult to predict; they cannot be relied on to act in their own best interests, let alone to keep their agreements. Many regimes of this type do indeed eventually commit suicide one way or another, but they can cause untold harm along the way.
In fact, were it not for the likely human costs of such a venture, I could almost wish that this fruitcake Iranian regime would actually attempt to deliver on its threats, because I can think of no more effective prescription for regime suicide, and I'd dearly love the Teheran regime to join those of Gaddafi, Mubarak et al on the list of collapsed Middle Eastern dictatorships.