U.S. forces formally withdrew from Iraq on Wednesday, ending a two-decade military presence that stoked years of devastating bloodshed and leaves behind a battered nation struggling to unshackle itself from its two most powerful, and now warring, allies.

After toppling Saddam Hussein in 2003, the brutal dictator who ruled Iraq for nearly 24 years, American forces are making their second withdrawal from the country.

The U.S. invasion and subsequent occupation, which ended in 2011, left a country reeling from sectarian bloodletting and militant insurgencies that cost nearly 4,500 U.S. lives and killed more than 115,000 Iraqis, according to the most modest counts.

American forces ultimately returned three years later — this time to lead the fight against the Islamic State, the jihadist force that once seized swathes of Iraq and Syria and became notorious for its slaughter of Shiite Muslim Iraqis, public killings of hostages, and torture and enslavement of women from Iraq’s Yazidi minority.

With the end of Operation Inherent Resolve — the U.S. military’s official name for the multinational campaign against the Islamic State, or ISIS — the last of the 2,500 U.S. forces stationed in Iraq this year will depart.

Physical reminders of decades of war are being erased every day. The blast walls that once snaked through Baghdad have come down. Malls, restaurants and construction sites are buzzing in a country determined to reclaim the rhythms of normal life stolen by years of car bombs.

Iraqis’ hard-won gains look more precarious in a region convulsing from the turmoil of the U.S.-Israeli war on Iran. Iraq is struggling to navigate its critical relationships with Iran, its powerful neighbor, and with its most important ally, Washington, wary of letting the exit of American troops in the country embolden Tehran.

The U.S. withdrawal agreement was struck between the Baghdad government and the Biden administration in 2024. That President Trump’s administration followed through with the Sept. 30 deadline — despite the war with Iran — reflects broader U.S. determination to step back from the region.

For years, there has been widespread American fatigue with so-called forever wars, as the conflicts in Iraq and in Afghanistan came to be known.

Even as Iraq commemorates the U.S. withdrawal this week with a three-day “celebration of sovereignty,” the country is under huge pressure from the Trump administration to disarm Iran-backed Shiite Muslim militias, many of which are defying state efforts to bring them under control.

The last U.S. forces leave a troubled American legacy. Iraq suffered huge numbers of civilian casualties and a cycle of sectarian violence between Iraq’s Shiite Muslim majority, empowered after years of repression by the Hussein government, and the Sunni minority, stripped of privileges it once held under his rule.

U.S. forces also committed many abuses themselves — including the torture of Iraqi detainees at Abu Ghraib and the use of private defense contractors like Blackwater, whose extrajudicial killings of civilians fueled deep resentments over American impunity.

Despite these grievances, Iraqis have been watching the U.S. departure with a sense of trepidation.

“My wife lost her eyesight from the shrapnel of an American bullet,” said Omar al-Husseini, a photographer from Mosul, the city at the heart of the Islamic State’s self-proclaimed caliphate. “My uncle was killed by ISIS, after being paralyzed by an American bullet. But today, when we speak about the Americans’ departure, our happiness is mixed with fear.”

Under the leadership of the novice prime minister, Ali al-Zaidi, Iraq faces the daunting task of reining in the vast array of militias.

First established with Iranian support to fight the U.S. occupation, the militias killed hundreds of American soldiers, and the sectarian bloodshed they helped foment killed tens of thousands of Iraqis. In 2014, when Iraqi Shiites mobilized to fight the Islamic State, the militias multiplied. In the years since, the thousands-strong militias have grown in power — not only through military might but also by forming political parties that deeply embed them in the state.

Mr. al-Zaidi has pledged to bring the militias under state control by mid-2027. But it is far from clear that he can deliver. The stakes are high: Through Iraq’s U.S.-based bank account for oil payments, Washington controls the physical shipment of dollars Iraq earns and has shown itself willing to use that power after temporarily halting the flow this year.

Iran is determined to preserve the militias, which have proved to be valuable partners in launching strikes during the war, in sowing regional chaos and in inflicting drastic costs on the global economy.

In a recent New York Times interview, Mr. al-Zaidi said, “Every Iraqi today wants his country to have complete sovereignty; they want power to be exclusively in the hands of the state,” and he pledged to end “the law of the jungle.”

The unforeseen consequences of withdrawal

Many Iraqis worry how their country will fare in this struggle.

“We fear Iraq could be swallowed up,” said Ahmad al-Shammari, an employee at the ministry of education in Falluja, a city that came to symbolize the fragile victories of the first American military presence in Iraq.

Falluja suffered the deadliest and most destructive battles to crush insurgents during the U.S. occupation, only to become the first city to be seized as Islamic State militants swept the country in 2014.

When the U.S. forces returned to spearhead a multinational coalition to defeat the jihadist force, the struggle to rout the Islamic State reduced huge parts of Iraqi cities to rubble.

It left an untold number of dead, displaced millions from Iraq’s Sunni minority and brought many more years of sectarian strife.

The question for many ordinary Iraqis today is what unforeseen consequences this latest U.S. departure may have on their lives, whether that is a jihadist resurgence or the state’s imminent confrontation with Iran-backed militias.

“I remember what happened after the withdrawal in 2011,” said Sarkawt Ahmad, a 26-year-old shopkeeper in northwestern Sulaymaniyah, in the Kurdistan region of Iraq. “Imagine what these pro-Iranian groups will do to us in the absence of the international coalition.”

Some regional security experts argue that it was the continued U.S. presence in Iraq that allowed Iran-backed militias to justify their existence, and their arms.

“We can’t just shape-shift these missions from one raison d’être to another, which is what we’ve done for 25 years,” said Adam Weinstein, a longtime proponent of U.S. forces’ ending their mission in Iraq who is the deputy director of the Middle East Program at the Quincy Institute, a research group.

Referring to the withdrawal, Renad Mansour, an Iraq analyst at Chatham House, a research institute based in London, said, “In the bigger picture, this shows the U.S. is no longer what it used to be — but, also, its priorities are no longer what they used to be.”

Kurds are vulnerable under a new security order

The United States and Iraq have still not hammered out final plans for their security relationships moving forward.

The situation has particularly unnerved Iraq’s semiautonomous Kurdistan region in the north, which saw how the Trump administration’s withdrawal of U.S. forces from Syria’s Kurdish-controlled northeast forced the region to come under central government control.

Iraqi Kurds, who began establishing sovereignty in their region through U.S. air support in the 1990s, feel the most vulnerable under Iraq’s new security order. As one of the closest U.S. security partners in the region, Iraqi Kurdistan has come under repeated attacks by Iran and its allied Iraqi militias this year.