Whenever the Iran war comes to an end, the Islamic Republic is likely to emerge in a stronger position. Should the terms of a June memorandum of understanding be met, Western governments would lift many sanctions on Tehran and the country would gradually be reintegrated into the global economy. Iranian control of the Strait of Hormuz, once an open waterway, might be formalized through some kind of joint tolling system. And Iran might be free to reconstitute its ballistic missiles and drone capabilities, weapons that proved very useful in the most recent months of fighting.

But at least in one area, the war has left Iran notably weaker: Iraq. Ever since the toppling of the Iraqi dictator Saddam Hussein in 2003, Iran has been able to exercise a great deal of influence over its western neighbor. It has embedded itself within Iraq’s Shiite political establishment, mediating between rival factions, shaping successive governments, and using Iraq to gain hard cash through smuggling and currency exchange networks. Iran supported many of the Iraqi paramilitary groups that helped defeat the Islamic State, also known as ISIS, in 2017. Iraqis still grew to resent Iran’s overweening influence in their country, not least because of the involvement of Iranian-backed militias in a brutal crackdown on anticorruption protesters in 2019 and 2020. Now, the tumult of recent months has further tilted Iraqis against Iran’s desire to make their country a staging ground of resistance to the United States and Israel. Leaders of political parties and militia groups that once hewed close to Tehran are pulling away.

In early June, fighters from Saraya al-Salam, a militia loyal to the Iraqi Shiite cleric Muqtada al-Sadr, gathered in the city of Samarra to hand over their weapons to the Iraqi government. That disarmament marked the group’s withdrawal from the Popular Mobilization Forces, a powerful umbrella coalition of mostly Shiite militias that exists at once inside and outside the Iraqi state. Saraya al-Salam’s thousands of fighters were the first to pull out of the alliance, and they have not been the last: Asaib Ahl al-Haq, a powerful Iranian-backed militia, announced that it, too, would leave the PMF.

Several prominent Iranian-backed militias remain doggedly committed to advancing Tehran’s interests in Iraq and the wider region. But the splintering of the PMF is a real blow to Iran. The so-called axis of resistance, Iran’s network of proxies across the region, has been badly damaged since Hamas’s October 7, 2023, attacks on Israel and Israel’s subsequent campaigns in Gaza and Lebanon. But in Iraq, the Iranian-aligned militias had largely stayed out of the fight and maintained their........

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