The first hours of Operation Epic Fury—the joint U.S.-Israeli military offensive against Iran, launched on February 28—demonstrated the extraordinary reach of modern precision warfare. U.S. and Israeli strikes killed Iran’s supreme leader, Ayatollah Ali Khamenei, along with senior commanders of the Islamic Revolutionary Guard Corps and key intelligence officials, in what Washington and Jerusalem described as a decisive blow intended to cripple Tehran’s command structure and destabilize the regime.

Yet within hours, any hope that the precise decapitation strikes would limit the scope of the war was dashed. Iran launched hundreds of ballistic missiles and drones not only at Israel but also across the Gulf. Air raid sirens sounded in Tel Aviv and Haifa. Missiles slammed into interceptors over Doha and Abu Dhabi. At Al Udeid Air Base, in Qatar—the forward headquarters of U.S. Central Command—personnel took shelter as interceptors streaked overhead. Air defenses flashed into action at U.S. bases at Al Dhafra in the United Arab Emirates and Ali Al Salem in Kuwait. Prince Sultan Air Base in Saudi Arabia reported incoming drones. Near the U.S. Fifth Fleet headquarters in Bahrain, naval forces were placed on heightened alert.

The Iranian response has had enormous ramifications for the Gulf, killing civilians, shuttering airports, threatening shipping and oil exports, and tarnishing the region’s image of stability and safety. An iconic hotel on the waterfront in Dubai caught fire after debris from an intercepted drone fell into its upper floors. Kuwaiti authorities reported damage near civilian airport facilities. According to news reports, several tankers have been struck near the Strait of Hormuz, prompting a spike in insurance premiums for shipping through the Gulf. Soon after the conflict erupted, oil futures jumped sharply as traders priced in the risk of sustained disruption to one of the world’s most critical energy chokepoints.

Iran’s strikes cannot be dismissed as acts of scattered retaliation, the flailing lashing out of a dying regime. Rather, they represent a strategy of horizontal escalation, a bid to transform the stakes of a conflict by widening its scope and extending its duration. Such a strategy allows a weaker combatant to alter the calculus of a more powerful foe. And it has worked in the past, to the detriment of the United States. In Vietnam and Serbia, U.S. adversaries responded to overwhelming displays of American airpower with horizontal escalation, eventually leading to American defeat, in the former case, and, in the latter, frustrating U.S. war aims and spurring the worst episode of ethnic cleansing in Europe since World War II. Decapitation strikes, in particular, create powerful incentives for horizontal escalation: when a regime survives the loss of its leader, it must demonstrate resilience quickly by widening the conflict. Although the United States has hugely battered Iran, it must reckon with the implications of Iran’s response. Otherwise, it will find itself losing control of the war it started.

Horizontal escalation occurs when a state widens the geographic and political scope of a conflict rather than intensifying it vertically in a single theater. It is especially appealing as a strategy for the weaker parties in a military contest. Instead of trying to defeat a stronger adversary head-on, the weaker side multiplies arenas of risk—drawing additional states, economic sectors, and domestic publics into the remit of the conflict. Iran cannot defeat the United States or Israel in a conventional military contest. It does not need to. Its objective is to gain greater political leverage.

The strategy of horizontal escalation follows a recognizable pattern. First, Iran has demonstrated resilience. U.S. decapitation strikes intended to paralyze the Iranian military. By launching large-scale retaliation within hours of losing the supreme leader and many senior commanders, Tehran signaled continuity of command and operational capacity.

Second, Iran has widened the conflict well beyond Iranian territory, effecting what scholars call “multiplication of exposure.” Rather than confining retaliation to just Israel, Iran struck or aimed at targets in at least nine countries, most hosting U.S. forces: Azerbaijan, Bahrain, Greece, Iraq, Jordan, Kuwait, Qatar, Saudi Arabia, and the United Arab Emirates. The message was unmistakable: those countries that host American forces would face severe consequences and the war that Israel and the United States started will spread.

Decapitation strikes create powerful incentives for horizontal escalation.

Third, Iran has politicized the conflict through its strikes. Iran’s retaliation has resulted in the closure of airports, the burning of commercial property, the........

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