US forces leave Iraq, raising concerns over stronger Iran-backed groups and Islamic State resurgence

US forces withdrew from their remaining bases in Iraq on Wednesday, raising concerns about a potential security vacuum that could strengthen Iranian-backed Shi'ite militias and provide the resurgent Islamic State with an opportunity to regroup.

The withdrawal, hailed as a victory by Tehran and its allies, was agreed in 2024 under then-President Joe Biden and implemented by Donald Trump's administration even as Washington wages war against Iran. The move comes 23 years after the US-led invasion toppled Saddam Hussein, setting off years of turmoil that ultimately contributed to the rise of Islamic State.

As US troops leave neighbouring Iraq, Iran's Islamic Revolutionary Guard Corps urged Americans to vote against Trump's allies in Congress. Tehran has steadily expanded its influence in Iraq through allied militias since the fall of Saddam.

Although the departure of US forces is widely welcomed by Iraqis, some remain concerned that Iraqi security forces, despite years of US training and support, may struggle to fully protect the country. About 4,500 US service members died during more than two decades of war in Iraq.

"The lesson from the past two decades is that security vacuums can be extremely dangerous," said Jassim al-Bahadli, an Iraqi analyst who advises security forces.

US troops invaded Iraq in 2003, subsequently occupying the country, helping establish a Shi'ite-led government and fighting a prolonged insurgency involving Saddam loyalists and al-Qaeda. A devastating sectarian conflict followed before US forces withdrew in late 2011.

They returned less than three years later to support Iraqi forces in defeating Islamic State, the Sunni militant group that terrorised millions during a major conflict from 2014 to 2017.

Nearly twice as many US service members were killed in the Iraq war, known as "Operation Iraqi Freedom", as in the parallel conflict in Afghanistan, which ended with a US withdrawal in 2021.

During this year's conflict with Iran, seven of the 18 US service members reported killed were in Iraq. The most recent was an Army sergeant who died in July while carrying out the controlled detonation of a drone at a base near Erbil.

Iran and its allies see gains

Iran, which says its ultimate goal is to force US forces out of the Middle East, has portrayed the withdrawal from Iraq as a victory for its "axis of resistance" — a network of allied armed groups across the region.

"What's particularly concerning is not necessarily direct Iranian intervention, but the possibility that Iran's proxies will feel increasingly empowered in the absence of a Western military presence," said Baghdad-based political analyst Ahmed Younis. "These groups may attempt to expand their role in shaping state policies and consolidating their presence within key institutions."

Iraqi security officials in both the federal government and the semi-autonomous Kurdish region have also warned that the US withdrawal could create opportunities for Islamic State fighters. Although the group lost its self-declared caliphate nearly a decade ago, it continues to maintain a network of sleeper cells.

At its peak, Islamic State controlled roughly one-third of Iraq and killed thousands of people, including hundreds whose executions were filmed at a former US military base.

US forces had provided Iraqi security agencies with vital intelligence on Islamic State activity, along with aerial surveillance and reconnaissance.

"The most important question now is whether Iraq's security institutions have prepared a viable Plan B for the post-coalition phase," said retired Iraqi Army General Mohammed al-Jubouri, who commanded a brigade during the fight against Islamic State.

He warned that a worst-case scenario would involve Islamic State acquiring armed drones or improvised explosive drones while Iraq remains without sufficient air-defence capabilities to counter such threats effectively.