US President Donald Trump’s handling of the Iran crisis and the closure of the Strait of Hormuz underlines an old lesson: force without planning, consultation and legitimacy rarely ends well. History tells us that the effective use of force requires clear, limited objectives; legality; prior planning; committed partners; and, even then, a measure of good luck. Today, the United States is leaning heavily on that last ingredient.
Coalition building has never been easy, but when done well it is enormously powerful.
The Allied coalition in World War II, culminating in the Normandy landings, remains the benchmark for complex, combined operations planned painstakingly over years. The First Gulf War had a clear UN mandate, defined objectives and broad coalition. It showed how military force, properly framed and prepared, could reset a regional balance without becoming an open‑ended occupation.
For Western democracies, war as an instrument of policy should be a last resort, not a first impulse. War is, by definition, a failure of diplomacy and almost never ends as quickly or as cleanly as its architects hope. Even when initial objectives are achieved, unintended consequences can take years or decades to work through the international system. Those longer‑term costs are usually borne by allies, partners and civilians far from the initial decision‑making table.
That is why the use of force is the most serious order any government can give. In my experience, the threat of latent force—credible capability clearly aligned to political aims—is often more powerful than actual force. Once force is used and fails to achieve its aims, enemies tend to harden their resolve, publics polarise and conflicts become protracted. The decision to cross the threshold to the use of force should therefore be tied tightly to narrowly defined objectives and a plausible path back to diplomacy.
Force is best employed in support of diplomatic and negotiated outcomes with clear, limited aims. The First Gulf War remains a good example: the objective was to eject Iraqi forces from Kuwait and restore its sovereignty, not to march on Baghdad. Similarly, more recent, tightly scoped operations—such as targeted, time‑bound interventions to support political settlements in the Americas—have demonstrated how calibrated force can reinforce diplomacy rather than replace it. The test is always whether the operation supports a political strategy, not the other way around.
Legitimacy is central, especially for coalition operations. For democratic partners, effective use of force must comply with international law and the recognised rules of war if it is to be sustainable at home and credible abroad. Potential contributors will want to understand the legal basis for action, the arrangements that will grant their forces appropriate immunities and protections, and the parameters under which their troops will operate before they commit. These are the foundations upon which trust between governments, militaries and publics is built.
Australia’s leadership of the Regional Assistance Mission to Solomon Islands is instructive. Even with a direct request from Honiara for military and police intervention to restore law and order, Australia and its partners sought the endorsement of the Pacific Islands Forum, relevant Solomon Islands legislation and the support of the United Nations before deploying. This careful attention to legality and legitimacy at the low end of the conflict spectrum gave partners confidence that their forces were being committed to a just and properly constituted mission, even though the operation contemplated the potential use of force.
The present US operations in Iran sit much closer to the high end of the conflict spectrum but appear to lack a comparable foundation in international law and legitimacy. They also appear to have proceeded with minimal prior consultation with key allies who are now being asked, after the fact, to join a mission to keep the Strait of Hormuz open. This is a poor basis upon which to build a coalition, particularly when significant and arguably foreseeable second‑order effects have already materialised, including the disruption of a waterway that carries around one fifth of the world’s oil.
Military operations of this scale require detailed planning to ensure that force is applied legally, ethically and in a way that has a realistic chance of achieving the desired policy outcomes. Planning is a crucial military asset. Good planners think not only about the most likely outcome but also about the most dangerous plausible outcome. In the current case, it is hard to imagine any responsible planning process that did not identify the closure—or effective closure through threat—of the Strait of Hormuz as both likely and dangerous. That, in turn, raises hard questions about the extent and quality of the contingency planning undertaken and about why close allies were not brought into that planning well before the first strikes were ordered.
Those questions are not academic. The US decommissioned its last dedicated mine countermeasures ships in the Middle East in 2025 and is still in the early stages of deploying new mine countermeasure capabilities on littoral combat ships and unmanned systems. Britain, by contrast, maintains advanced minehunting capabilities and is now weighing the deployment of minehunter drones and naval assets to help reopen the strait at the US’s request. Asking allies to fill critical capability gaps after operations have commenced, and after global fuel prices have already spiked, is not a formula for enthusiastic burden‑sharing.
The domestic repercussions for the US are also likely to be significant. Rising global oil prices have already translated into sharply higher fuel prices for American consumers, and this is one issue on which US public opinion is remarkably united. Meanwhile, major strategic competitors stand to benefit from higher energy prices and further distraction of US attention and resources.
Effective use of force rests on five pillars: clear and limited objectives, legal and moral legitimacy, rigorous prior planning, genuinely committed partners and, inevitably, some good luck. History suggests that when the first four are in place, nations can often make their own luck. In the ongoing Iran crisis, Trump will need a great deal of good luck to prevent events in and around the Strait of Hormuz from sliding further out of control, because the other four pillars appear worryingly weak.
