The drumbeat of war with Iran grows steadily more intense. Each day brings more defiant rhetoric from Tehran, another failed UN nuclear inspection, reports of western military preparations, an assassination, a missile test, or a dire warning that, once again, the world is sliding towards catastrophe. If this all feels familiar, that's because it is. For Iran, read Iraq in the countdown to the 2003 invasion.

A decisive moment may arrive when Barack Obama meets Israel's prime minister, Binyamin Netanyahu, in Washington on 5 March. "The meeting … will be definitive," said Ari Shavit in Haaretz. "If the US president wants to prevent a disaster, he must give Netanyahu iron-clad guarantees the US will stop Iran in any way necessary and at any price after the 2012 [US] elections. If Obama doesn't do this, he will obligate Netanyahu to act before the 2012 elections."

If accurate, this is not much of a choice. It suggests military action by the US or Israel or both is unavoidable, the only question being one of timing. Objectively speaking, this is not actually the position. All concerned still have choices. The case against Iran's nuclear programme is far from proven. It is widely agreed that limited military strikes will not work; a more extensive, longer-lasting campaign would be required. And Obama in particular, having striven to end the Iraq and Afghan wars, is loath to start another.

But as with Iraq in 2003, the sense that war is inevitable and unstoppable is being energetically encouraged by political hardliners and their media accomplices on all sides, producing a momentum that even the un-bellicose Obama may find hard to resist.

A recent analysis of US public opinion revealed deeply ambivalent attitudes on Iran, with the majority of Americans apparently favouring diplomatic solutions. Yet as Republican presidential candidates exploit the issue, as the Israelis lobby America, and as Iranian factions manoeuvre ahead of parliamentary polls, the likelihood grows that doves and doubters will again be either converted or ignored.

In some key respects, the Iran crisis is distinctly different from that over Iraq in 2002-03. As matters stand, similarly strident warmongering surrounding Iran is thus hard to understand or explain – unless the ultimate, unstated objective is not to curb Iran's nuclear programme but, as in Iraq, to overthrow its rulers.

Bogeymen

George Bush and Tony Blair claimed a moral imperative in toppling the "monstrous" dictatorship of Saddam Hussein. But the much vilified Mahmoud Ahmadinejad, Iran's president, is no Saddam, and neither is the country's bumbling Supreme Leader, Ayatollah Ali Khamenei. The Iranian regime is repressive and sporadically brutal, but so too are many developing world governments. Unlike Saddam's Ba'athists, it has significant democratic and ideological underpinning. As a bogeyman whose depredations might justify international intervention, Ahmadinejad is a flop.

Weapons of Mass Destruction

Saddam, notoriously, had no deployable or usable WMD, but his overthrow was primarily justified by the mistaken belief that he did. The present western consensus is that Iran is seeking nuclear weapons capability, but does not have an atomic bomb and is not currently trying to build one. Khamenei said this week that nuclear weapons were "useless and harmful" and that possessing them was sinful . Netanyahu's belief that Israel faces an imminent, existential threat is visceral rather than fact-based. Israel's refusal to acknowledge its own nuclear arsenal, let alone contemplate its reduction, further undermines the case for action.

Terrorism

Plenty of evidence exists that Iran supports, or has supported, armed militants, jihadis, and anti-Israeli and anti-western armed groups in Palestine, Lebanon, Syria, Iraq and Afghanistan, providing financial and political backing, arms and training. In this respect, its behaviour is more threatening to western interests than was that of Saddam's secular regime, no friend to Islamists. But limited or even protracted attacks on Iran's nuclear and/or military facilities would not end these links, unless there was a shift of political direction in Tehran.

Strategic power-games

Iraq was considered important for its strategic position at the heart of the Arab Middle East and its economic potential, especially its oil reserves. Similarly, there can be no doubt the US and Britain would like to see energy-rich Iran return to the western camp, as in the pre-revolution days of the Shah. Conversely, Iran's military is more powerful and more committed to the defence of the status quo, from which it benefits greatly, than was Iraq's. The potential disruption to oil supplies and western economies, not to mention the impact of asymmetric Iranian counter-attacks, makes a resort to war contingent on producing lasting dividends.

Political imperatives

In contrast to the splits over Iraq, the main western powers are united in their determination to bring Iran to heel. As well as Netanyahu, David Cameron, Nicolas Sarkozy and Barack Obama have all declared an Iranian bomb unacceptable. Their inflexibility thus makes war more rather than less likely should Iran refuse to back down. "Having made the case for urgency and concerted action, it would be difficult for Obama to tell the world 'never mind' and shift to a strategy that accepts Iranian membership in the nuclear club," said Michael Gerson in the Washington Post.

In short, the Iranian crisis differs from that over Iraq in 2003 in key respects. But the current impetus towards war can only be explained in terms of a western desire for Iraq-style regime change – because only regime change may achieve the de-nuclearisation the west insists upon.