When the United States attacked Iran on 28 February, it was betting on a swift victory that would bring about regime change. President Trump’s military engagements have generally been quick operations in pursuit of a clear goal, such as the kidnapping of Nicolás Maduro or the bombing of Iranian nuclear facilities in June 2025. The American president is a harsh critic of past US foreign wars, and it would not be true to his character to knowingly involve the country in a protracted military conflict. And, indeed, the first day of Israeli-American attacks began with the killing of the Supreme Leader, the commander of the Revolutionary Guards (IRGC), the chief of staff of the armed forces, the minister of defence, and the secretary of the Defence Council – a decapitation strike aimed at achieving a quick triumph. Yet after the first day, the administration’s predictions of a month-long operation stretched to eight weeks, and the Pentagon is now preparing for a campaign that could last more than 100 days and well into summer. Trump has also walked back his rhetoric on regime change. The Islamic Republic has been putting up a fight.

Much of this stems from how the Islamic Republic was built and functions. Its dispersed power structure, unconventional military forces, and ability to impose significant costs on the US and its allies make it a far more difficult target for regime change – especially foreign-led. This sharply contrasts with other regional cases, from Saddam Hussein’s Iraq and Muammar Qaddafi’s Libya to Bashar Assad’s Syria. These regimes, though disintegrating under vastly different circumstances with varying degrees of foreign intervention, were all deeply personalistic. This is why the US launched a (failed) decapitation strike against Saddam before sending ground troops, why NATO air-strikes targeted Qaddafi himself, and why, once Assad fled Syria, his entire political system collapsed.

Trump appears to have approached Iran through a similar lens, viewing the regime as personalistic and hierarchical. The likely expectation was that the removal of Ali Khamenei and the top brass of military leadership, combined with sustained strikes on military infrastructure, would trigger a reaction: the collapse of a newly headless regime, the emergence of a more pliant successor no longer bound to Khamenei, or even mass unrest in light of the recently brutally repressed protest movement and widespread public hatred of the regime.

This did not happen: instead, the regime has proven itself to be resilient, and it has been inflicting heavy costs on the United States and its allies. US intelligence itself in a classified report from a few weeks ago – one whose findings are at odds with Trump’s actions – stated that large-scale war on Iran would be unlikely to produce regime change. This is because the Islamic Republic is fundamentally different from the highly personalised autocracies that have collapsed elsewhere in the region. Unlike those regimes – and even unlike the pre-1979 monarchy – the Islamic Republic is not organised around a single person: its institutional design prioritises not the fate of any leader, but rather the preservation of the system itself.

A look at the Islamic Republic’s decision-making apparatus sheds light on how this plays out in practice. The Supreme National Security Council (SNSC) provides a clear example. The SNSC brings together different regime elites, including military officials (army and IRGC commanders), key ministers (intelligence, foreign affairs, interior), the president, and other key figures, such as Ali Larijani and Saeed Jalili. The SNSC effectively serves as the central body responsible for formulating core policies on national security – from the nuclear issue to the defence of Iran’s borders. Through the SNSC, senior regime officials deliberate and make decisions through consensus, decisions that are formally ratified by the Supreme Leader. Decision-making thus occurs through an institutionalised and collegial process rather than through unilateral directives from the top. The Defence Council, newly formed under the SNSC after the 12-Day War, comprises IRGC and army commanders, along with representatives of the intelligence ministry, and functions similarly but with a particular focus on national defence.

This institutionalisation of power makes the regime considerably less susceptible to collapse following decapitation. Even if key members of bodies like the SNSC or Defence Council are killed, such as Hossein Salami, the commander-in-chief of the IRGC who was killed in the 12-Day War, or Mohammad Pakpour, Salami’s replacement who was killed two weeks ago, they can be replaced. Likewise, Khamenei’s death produced little functional change in the system and nor would the death of his son and successor, Mojtaba Khamenei, or of other prominent figures such as Ali Larijani. Decision-making and authority in the Islamic Republic do not hinge on a single person: the system was built to function beyond individuals.

The regime’s armed forces are similarly depersonalised and horizontal. Each of Iran’s 31 provinces has an independent IRGC chain of command; provincial units can act independently of central command; and weapons stockpiles are spread throughout the country, accessible to these different units. Now, in wartime, local commanders have been empowered under Iran’s ‘Mosaic Defence’ policy, which enables them to act independently, especially if senior leaders are killed or communications are cut. This policy of local independence has a long history within the IRGC, beginning in 1979 itself. When suppressing the Iranian Kurdish conflict immediately after the revolution, IRGC fighters benefitted from a decentralised structure based in part on direct action at a local level. This continued to shape the IRGC during the Iran-Iraq War and remains a defining feature of the organisation.

The way in which the IRGC actually fights – by air, sea, or land – is indicative of this. Though Israel and the US have control of the Iranian skies, Iranian unconventional aerial weapons have been able to wreck havoc on US allies. Even if Washington succeeds in degrading Iran’s missile stockpiles, much of Iran’s campaign – especially in the Arabian peninsula countries, where it has been inflicting the most damage – comes from drones, which are inexpensive, easy to produce, and can be launched from anywhere in the country. And though President Masoud Pezeshkian seemed to imply that Iran would stop such operations, this does not seem to be happening.

Trump has also spoken about destroying the Iranian navy. Yet if the Iran-Iraq War demonstrated anything, it is that the IRGC’s naval forces are more dangerous when acting unconventionally. During that war, for example, the IRGC navy engaged in swarming tactics, attacking tankers with small, lightly-armed boats designed to surprise enemy forces, tactics that, since the war, the IRGC has only refined. Thus, the fact that Iranian conventional naval forces have been decimated and that the regime is relying primarily on speedboats might not be the victory that Trump is claiming it to be: the IRGC’s navy was never designed to compete conventionally with a country like the US.

A potential US or Israeli ground invasion would confront an institution shaped by guerrilla warfare – a tough opponent for conventional armies. The IRGC emerged as an amalgamation of revolutionary militias, and several of its early commanders, such as Abbas Aghazamani and Mohammad Montazeri, gained their first military experience in Palestinian Liberation Organization (PLO) camps under commanders who themselves had undergone training with Vietnamese guerrillas, whose campaign of low-intensity warfare forced the US to withdraw during the Vietnam War. Though the IRGC could never defeat the US outright, it could impose substantial costs and outlast it (which, in itself, would be claimed as a victory by the Islamic Republic). Short of a massive ground invasion – one dwarfing that deployed in Iraq in 2003 – the United States would struggle to decisively defeat it. If Iranian Kurdish forces were to lead such an invasion with US aerial support – an idea floated but then denied by Trump – the outcome might differ, given the Kurdish parties’ experience in guerrilla warfare. Yet Kurds make up only about ten per cent of Iran’s population, and entrenched anti-Kurdish sentiment in Iran’s Persian-speaking provinces might preclude the emergence of a nationwide anti-regime movement led by the Kurds.

This is not to suggest that the Islamic Republic or the IRGC in particular cannot be defeated. This decentralised and unconventional system carries its own vulnerabilities, including the possibility of defections by individual IRGC units, which would be essential to regime change. In principle, the United States and Israel could also use their overwhelming military superiority to continue bombing Iran until the state eventually collapses. Yet such an outcome would not come quickly. The Islamic Republic’s dispersed power structure, unconventional military forces, and capacity to absorb punishment make it a very difficult opponent. Defeating such a system would therefore require not a swift campaign but, at best, a prolonged and costly war of attrition. This may prove difficult for the American president to sustain politically, especially as his party faces looming midterm elections while he struggles to gain popular support for his war.