US forces have finally quit Iraq. What happens now?

Baghdad: US military forces pulled out of Iraq on Wednesday following two decades of American involvement that resulted in the deaths of hundreds of thousands of Iraqi civilians and thousands of US troops, and now leaves a battered but increasingly influential Iran at the centre of the region’s future.

The withdrawal concludes a Biden administration agreement made in 2024 to zero out US military personnel in Iraq by this year. Recently, there were about 1500 combined US personnel and anti-Islamic State coalition members in Iraq, a US official said, as forces consolidated and departed ahead of the September 30 deadline.

That mission will continue in Jordan, from where the Pentagon says it can target militants who pose a threat to US personnel and interests, the official said, speaking on the condition of anonymity to discuss military planning.

The redeployment of US forces has been a muted event in Washington. The 2003 invasion triggered a significant human and financial toll that will be felt for generations. As many as 210,000 Iraqi civilians were killed between the invasion and 2023, along with 4599 US service members, according to figures from Brown University’s Cost of War Project.

Roughly 170,000 US troops were in the country at the height of the war in 2007, when sectarian violence spiralled out of control. President Barack Obama vowed to end the unpopular conflict after he was elected in 2008. He declared an end to combat operations and an eventual pullout in 2011.

The Islamic State, born of al-Qaeda militants and other extremists, blitzed across Iraq and Syria in 2014, prompting Obama and an international coalition to re-enter the region in a campaign that lasted into the first Trump administration.

The decades of conflict has cost US taxpayers more than $US2.8 trillion ($4 trillion), Brown estimated, including related veterans care and operations in Syria.

Iraq emerged from the conflict with the Islamic State with a growing economy and a quasi-democracy that has been tested by religious sects in the government, particularly those with close ties to Tehran.

The US departure has been celebrated as a victory in Iran, which remains in an uneasy ceasefire with the US and Israel following months of war.

Iran has long taken advantage of Iraq’s destabilisation, seeding the government with friendly officials and arming militia groups that have expanded Tehran’s influence.

Mohammad Bagher Ghalibaf, Iran’s parliamentary Speaker, remarked on the US withdrawal last month during a diplomatic visit to Baghdad that included a visit to the site where Iranian commander Qasem Soleimani was killed in a US strike in 2020.

“The resistance front is the one prevailing now,” he said at a news conference, referring to cross-border Iranian political and military groups.

The fighters were organised under an umbrella group called the Popular Mobilisation Forces to confront the Islamic State. They are on Iraqi military payrolls but serve as Iranian proxy forces, numbering more than 200,000, analysts have said. They have fielded one-way attack drones and missiles to attack US troops and other adversaries.

The September 30 departure of US forces was meant to coincide with the disarmament of those Iranian-backed militia groups, which have largely ignored or defied the calls to disband. The timeline for the militias to disarm has been extended to June 2027, Iraqi Prime Minister Ali al-Zaidi has said.

Iran might be boosted by the US withdrawal, but its recent behaviour in the region had also created unlikely alliances against Tehran that challenged its power, said Mark Cancian, a senior adviser with the Centre for Strategic and International Studies think tank.

The 2003 operation that toppled Saddam Hussein threw Iraq into chaos, eliminating Tehran’s adversary on its western border, Cancian said. But its targeting of countries that house US troops during the Iran war had pushed some nations such as Saudi Arabia closer to Israel, Cancian said, creating a bulwark that was “unimaginable” decades ago.

“That’s a great help for the United States,” he said, “because we always had difficulty in balancing the Arabs and the Israelis.”

US forces in Jordan will focus on Islamic State militants. If the group “metastasises to something beyond [Iraq and Syria’s] control, and they want our help, then we’ll come in and help them,” the US official said.

Iranian-allied militias in Iraq have for years targeted Americans in the region, escalating attacks after Israel launched its devastating campaign in Gaza. Three US soldiers were killed in one such attack in Jordan in 2024.

“We only went after [Iranian-backed militants] in response to attempted attacks on our people,” the US official said. But overall, contending with those groups would henceforth be an “Iraqi responsibility”.

Iran’s hard-line Islamic Revolutionary Guard Corps has recently evolved its paramilitary operations in Iraq, which may pose difficulties for Baghdad, according to a senior official in the Iraqi prime minister’s office.

The IRGC had focused its resources in Iraq on smaller cells outside the larger militia networks to evade detection and deterrence, the official said, speaking on condition of anonymity to discuss sensitive security matters. The recent disarmament process has highlighted concerns about splinter groups.

The Iraqi official said, for instance, that the Iranian-backed militia group Asa’ib Ahl al-Haq turned over only about half the arsenal it was estimated to have, with its leaders saying the rest had been claimed by defectors who formed a new militia.

That new organisation received substantial Iranian support, had co-operated with Houthi allies in Yemen and was involved in recent attacks on energy infrastructure in Saudi Arabia, the official said.