As the United States’ five-month-old war with Iran continues to evolve, Tehran’s ability to continue punishing the United States and its allies has come as a surprise to many strategists and analysts. For months, the United States and Israel have intermittently pummeled the country with air strikes, decapitating much of its senior leadership. Yet Iran and its regional allies have proved remarkably dogged: Hezbollah remains a threat despite Israel’s blistering campaign in southern Lebanon, Iran-backed Iraqi militias have attacked Gulf oil and gas infrastructure, and the Houthis in Yemen have restarted their campaign against commercial ships in the Red Sea.

In fact, the resilience of both the Islamic Republic and its partners despite years of apparent setbacks points to an underlying flaw in the thinking that led to the conflict. In launching the campaign against Iran in late February, the United States and Israel were drawing on a theory pushed by American regime-change advocates and Israeli strategists for years: by targeting the Islamic Republic’s economy, its leadership, weapons facilities, and central supply lines with military force and economic sanctions, Washington could fatally undermine the Iranian regime. In doing so, it would also deal a decisive blow to the regime’s allies. Sever the head of the octopus in Tehran, the theory went, and the axis groups—the octopus’s many arms—would shrivel and die, too.

Two decades ago, a military campaign motivated by the so-called octopus doctrine might have worked. At that point, the relationship between Iran and its allies was less complex, with arms, technology, and know-how all routed through Tehran. But the axis is no longer organized as a simple system with easily identifiable points of failure. Today, it more closely resembles a densely interconnected, self-reproducing web, in which knowledge, resources, and even decision-making can be pooled in many different places at the same time. When a leader is killed, a manufacturing site or warehouse is bombed, or a supply line is cut off, the various groups that are involved adapt, quickly replacing the slain leader, filling in technical knowledge gaps needed to build weapons, and reconstituting supply lines via alternative routes. It is this increasingly sophisticated and flexible structure that has allowed Iran’s allies to adapt in the years since Hamas’s October 7 attacks. Even after Israel’s devastation of Hamas and Hezbollah during the war in Gaza and the collapse of the Assad regime in Syria—and even after the massive U.S.-Israeli air campaign against Iran this spring—the axis has remained largely intact.

As a result, Washington can no longer fall back on its go-to toolkit of escalating political pressure, sanctions, and military strikes. Outright defeat of Iran and the axis groups is likely out of reach, but limiting the threat they pose is still possible. Doing so will require the United States to develop a more comprehensive regional strategy aimed at addressing the complex international military, financial, and knowledge networks that now sustains Iranian power. Washington must now consider containing and potentially striking deals with Iran and its most powerful nonstate allies. And it must do whatever is necessary to limit the spread of the low-cost technology employed in the weapons systems designed by Iran and used by the axis, including engaging with China. This approach may not be satisfying to those American leaders who demand a resounding victory in the Middle East. But it stands a much better chance of success than the current strategy of attacking Iran over and over again and hoping that the Islamic Republic and its network of allies will eventually collapse.

Twenty years ago, the groups now known as the “axis of resistance” were mostly local insurgents using the tactics and technology of twentieth-century guerrillas. Under Iran’s tutelage, Hezbollah had emerged as a force in Lebanese politics and a powerful adversary to Israel, whose 2006 invasion it repelled using a stock of rudimentary short-range rockets and Iranian-made drones. Along with Iran, it also offered support to Hamas, which did not yet control Gaza. The Houthis were at the time a small insurgency hiding out in caves in northern Yemen, still a few years away from receiving meaningful support from Tehran. Iranian and Hezbollah operatives had just begun training Iraqi Shiite groups fighting U.S. forces in Iraq, teaching them how to organize insurgent cells, use small arms such as AK-47s and rocket launchers, and build roadside bombs.

In the decades since, Iran’s Islamic Revolutionary Guard Corps (IRGC) has developed a strategy for bringing these and other groups’ capabilities into the twenty-first century. Would-be axis members first receive........

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