For the past 17 years, the United States has maintained a military presence in Iraq. On Friday, Iraq’s prime minister asked the United States to send a delegation to discuss a mechanism for withdrawing U.S. troops. In response, the U.S. State Department said it was ready to “recommit to our strategic partnership — not to discuss troop withdrawal.”

More so than at any point since the rise of the Islamic State in 2014, foreign troop presence in Iraq is now in question. Iranian-backed militias and politicians want U.S. troops to leave to strengthen Iran’s influence, and many anti-government protesters, who have been filling Iraq’s streets for months, want both the United States and Iran out to overhaul the corrupt and sectarian political system set up after the U.S.-led invasion in 2003.

Analysts warn that this impasse will only strengthen the remnants of the Islamic State, which the United States says its troops are on the ground to combat. Friday’s back-and-forth between Washington and Baghdad came one week after the United States killed Iran’s top military strategist, Qasem Soleimani, in a drone strike in Iraq — a move that brought Iran and the United States to the brink of war and renewed calls for the removal of U.S. forces.

The United States has faced the drawdown debate before, and in 2011, President Barack Obama withdrew most U.S. troops, only to redeploy some starting in 2014 to fight the Islamic State. With withdrawal once again on the table, here’s a look at some crucial moments for U.S. troops in the course of America’s military presence in Iraq.

March 20, 2003: U.S.-led forces invade Iraq

Tens of thousands of U.S. troops deployed to Iraq for the battle to oust the country’s leader, Saddam Hussein. By April, U.S. forces had captured Baghdad, the capital.

May 1, 2003: Bush declares “Mission accomplished” in Iraq

It wasn’t. Between the start of the war and President George W. Bush’s declaration, 138 U.S. troops were killed in military operations in Iraq, according to Reuters. In the months that followed, political grievances erupted into sectarian insurgencies across the country as Sunni and Shiite militias fought for power among themselves and against occupying U.S. troops. Iraqi civilians bore the brunt of the deaths and destruction.

April 2004: Images released of U.S. soldiers abusing and torturing prisoners at Abu Ghraib

The photos — which “showed U.S. troops celebrating as prisoners were sexually humiliated and otherwise abused” — caused outrage around the world. Eleven U.S. soldiers pleaded or were found guilty of abusing detainees at the prison.

Sept. 7, 2004: U.S. military deaths in Iraq surpass 1,000

The grim milestone came as the Pentagon reported that Iraqi insurgents controlled key parts of central Iraq.

Nov. 7, 2004: The U.S.-backed battle for Fallujah begins

Thousands of troops participated in the subsequent fighting. U.S. and Iraqi operations to retake the city were the costliest and most intense in the Iraq War period from 2003 to 2011.

Oct. 26, 2005: Number of U.S. soldiers killed in Iraq surpasses 2,000

The Washington Post reported at the time: “Since the March 2003 invasion and quick march to take Baghdad, U.S. troops have been dying at about 800 a year, with most killed in action by crude but powerful roadside bombs and in firefights against an unrelenting insurgency. More than 90 percent of the deaths have come after President Bush declared an end to ‘major combat operations’ on May 1, 2003.”

Dec. 31, 2006: Death toll of U.S. military personnel surpasses 3,000

That same month, Saddam Hussein was put to death, after being captured by U.S. forces and tried by an Iraqi court. A Pentagon study from 2006 concluded that U.S. troops were losing the war.

Jan. 10, 2007: Bush announces troop surge

Facing heavy casualties and criticisms, Bush announced a fundamental shift in war tactics: a major troop buildup, or “surge,” which initially entailed the deployment of 21,500 more U.S. troops to support the embattled Iraqi government.

By June, the troop buildup was complete, with around 170,000 U.S. soldiers in Iraq marking the height of the surge.

April to June 2007: Deadliest quarter yet

According to Reuters, 331 U.S. soldiers were killed in the three-month period.

Sept. 16, 2007: Blackwater kills 17 Iraqi civilians

Guards with the private security company opened fire on civilians while accompanying a diplomatic convoy in western Baghdad. The event put a spotlight on the use of Western private security companies in the Iraq War, a sector not included in official troop counts.

March 28, 2008: Death toll of U.S. military personnel in Iraq exceeds 4,000

Most of the last 1,000 soldiers killed had been the victims of improvised roadside bombs, according to the New York Times.

Sept. 1, 2008: U.S. troops return control of Anbar province to Iraqi forces

It was a major milestone in the war, as the area had been the epicenter of the Sunni insurgency.

Nov. 17, 2008: Iraqi parliament ratifies timeline for U.S. troop withdrawal

The agreement stipulated that U.S. troops had to leave most Iraqi cities by summer 2009 and entirely pull out of Iraq by the end of 2011.

Feb. 27, 2009: Obama announces troop withdrawal by August 2010

The newly elected U.S. president said he planned to end combat operations by summer 2010, at which point around 50,000 troops would remain in the country to train Iraqi forces.

June 30, 2009: All U.S. combat troops leave Iraq’s urban centers

The deadline for U.S. troop withdrawal from Iraqi cities coincided with Iraq’s National Sovereignty Day.

Aug. 31, 2010: Obama declares end to seven-year combat mission in Iraq

After the major drawdown, 49,700 troops remained in the country.

Dec. 15, 2011: United States announces formal end to military mission in Iraq

The formal announcement that all troops would leave by the end of 2011 came after Washington and Baghdad failed to agree on a deal to govern U.S. deployments. Iraqi and U.S. officials did agree on 700 U.S. trainers staying on to work with Iraqi forces.

Overall, more than 1 million U.S. troops had served in Iraq since 2003.

June 15, 2014: Obama sends first troops to Iraq to fight ISIS

A small number of U.S. personnel had remained in Iraq in the intermittent years. That changed after the rise of the self-declared Islamic State, which seized large swaths of Iraq and Syria by 2014.

While insisting that the United States would not be part of combat operations, Obama announced that he was sending around 275 troops to aid Iraq’s battle against the group. That number soon rose to 800 — and kept climbing in the months and years that followed. U.S. officials, however, remained cagey about the exact numbers of troops deployed.

In August, the U.S.-led coalition began airstrikes against the Islamic State.

October 2015: First U.S. soldier killed in Iraq since the resumption of combat missions

By December 2015, there were 3,500 U.S. service members in Iraq.

April 18, 2016: Number of U.S. forces rises to around 5,000

Pentagon officials said there were 4,087 troops in Iraq. Analysts estimated that the number was closer to 5,000 when including military personnel guarding diplomatic outposts and waiting to rotate out.

Dec. 9, 2017: Iraq declares victory over the Islamic State

Iraq’s prime minister had declared victory in July after U.S.-backed Iraqi forces retook Mosul, concluding a bloody nine-month battle.

During the three years of fighting, Iraqi and U.S. forces found themselves almost back where they had been a decade before: fighting Sunni insurgents — this time in the form of the Islamic State — for control of places such as Mosul, Anbar and Fallujah that had also been major battlegrounds in the mid-2000s.

Dec. 27, 2019: American contractor killed in Iraq

At the end of 2019, more than 5,000 U.S. troops (in addition to contractors and subcontractors) remained in Iraq to help local forces contain the Islamic State and act as a counterweight to Iran’s influence in the region. To cap off the year, an Iranian-backed militia, Kataib Hezbollah, fired rockets at an Iraqi base housing U.S. troops, killing a U.S. contractor. The death of Nawres Hamid, an Iraqi American, set off a deadly wave of events: a U.S. reprisal attack on Kataib Hezbollah; Iran-backed militias storming the U.S. Embassy in Baghdad in response; the U.S. killing of Soleimani; and Iran’s decision to respond by firing ballistic missiles at U.S. forces in Iraq.

Jan. 10, 2020: Baghdad asks for pullout plan

After Trump’s decision to kill Soleimani, the future of the U.S. military presence in Iraq is once again an open question.

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