The United States officially intervened in the Syrian civil war on 22 September 2014 with the stated aim of combatting the Islamic State (ISIL/ISIS) militant organization. The intervention was part of Operation Inherent Resolve and saw the US support both anti-ISIL and anti-Assad factions, including the Syrian Armed Forces under the transitional government and the YPG-led Syrian Democratic Forces (SDF).

Shortly after the start of the civil war in 2011, the Obama administration placed new sanctions on Syria and supported the Free Syrian Army rebel faction by covertly authorizing Timber Sycamore under which the Central Intelligence Agency (CIA) armed and trained rebels. Following the Islamic State's occupation of Eastern Syria in August 2014, the United States conducted surveillance flights in Syria to gather intelligence on the group. In September 2014, the US-led coalition—which involved the United Kingdom, France, Jordan, Turkey, Canada, Australia, and others—launched an air campaign against the Islamic State and al-Nusra Front inside Syria.

The missile strike on Shayrat Airbase on 7 April 2017 was the first time the US deliberately attacked Syrian government forces during the war, with US forces proceeding to periodically attack Assad's forces and allies often in defense of either the SDF or the Syrian Free Army opposition group based in al-Tanf. In mid-January 2018, the Trump administration indicated its intention to maintain an open-ended military presence in Syria to accomplish US political objectives, including countering Iranian influence and ousting Syrian president Bashar al-Assad, however, on 19 December, President Trump unilaterally ordered the withdrawal of the 2,000–2,500 US ground troops in Syria at the time, which was to be completed in 2019. Concerns over a power vacuum resulted in the US instead leaving around 400 US troops garrisoned in Syria indefinitely, with any withdrawal being gradual and conditions-based, returning to a policy of open-ended US intervention in the country.

In 2019, the coalition saw decisive results in its intervention against the Islamic State; the terror group lost its last remaining territory in Syria during the battle of Baghuz Fawqani and its leader Abu Bakr al-Baghdadi died during a US special forces raid in Idlib in October 2019. The Trump administration ordered all US forces to withdraw from Rojava in early October ahead of a Turkish incursion into the region, a controversial move widely seen as a reneging of the US's alliance with the SDF in favor of NATO ally Turkey. However, by November 2019, US troops instead repositioned to eastern Syria, reinforcing their presence in the al-Hasakah and Deir ez-Zor governorates, with the subordinate mission of securing SDF-controlled oil and gas infrastructure from the IS insurgency and the Syrian government. On 23 November 2019, the head of US Central Command stated there was no "end date" on the US's intervention in Syria.

The US Department of Defense stated that there were around 900 US soldiers operating in Syria as of February 2021. On 19 December 2024, after the fall of the Assad regime, the Pentagon revealed that there were around 2,000 US troops in Syria, adding that the increase was temporary and occurred in recent months. However, the U.S. military continued to withdraw in 2025, leaving less than 1,000 troops to work with allies to fight the Islamic State militants. In February 2026, U.S. President Donald Trump ordered the complete withdrawal of American forces from Syria within the next two months. American forces completed their withdrawal on 16 April 2026, when US troops evacuated the Qasrak base in the Hasakah region, marking the end of more than a decade of American military presence in Syria. However, the conflict briefly continued about two months later when on June 19 the United States conducted an airstrike in Syria killing ISIS leader Ali Husayn al-Ulaywi, in a single post withdrawal strike.

Background

Leaked United States diplomatic cables have been seen as showing that regime change in Syria may have been a covert foreign policy goal of the US government in the years leading up to the civil war, even during the period when President Barack Obama was publicly engaging with Syrian president Bashar al-Assad. A 2006 memorandum by US diplomat William Roebuck of the embassy in Damascus stated:We believe Bashar's weaknesses are in how he chooses to react to looming issues, both perceived and real, such as...the potential threat to the regime from the increasing presence of transiting Islamist extremists. This cable summarizes our assessment of these vulnerabilities and suggests that there may be actions, statements and signals that the USG can send that will improve the likelihood of such opportunities arising. These proposals will need to be fleshed out and converted into real actions and we need to be ready to move quickly to take advantage of such opportunities. Many of our suggestions underline using Public Diplomacy and more indirect means to send messages that influence the inner circle.According to Seymour Hersh and activist Robert Naiman, Roebuck, who went on to be charge d'affairs of the Libyan embassy under Obama, also considered the advantages of promoting religious sectarianism in Syria.

Following the start of the Arab Spring in 2011, protests in Syria against the Assad regime were violently suppressed and a civil war began. By 2012 there were several armed opposition groups operating in the country, including the Free Syrian Army, formed in July 2011 by officers who defected from the Syrian Armed Forces. In 2012, the al-Nusra Front, led by Abu Muhammad al-Julani, was established by the Islamic State of Iraq (ISI) as the official branch of al-Qaeda in Syria. The al-Nusra Front was eclipsed by its own creator, and al-Qaeda severed its ties to the Islamic State of Iraq and the Levant in February 2014, after an eight-month power struggle. Despite clear connections between ISI and the al-Nusra Front, the two organisations never merged during the Syrian Civil War, as al-Julani refused to cede control to ISI and insisted on maintaining al-Nusra Front as a separate entity.

Shortly after the civil war broke out in 2011, the US initially supplied the rebels of the Free Syrian Army with non-lethal aid (e.g., food rations and pickup trucks), but quickly began providing training, money, and intelligence to selected Syrian rebel commanders. At least two US programs attempted to assist the Syrian rebels, including a 2014 Pentagon program that planned to train and equip 15,000 rebels to fight the IS, which was canceled in 2015 after spending $500 million and producing only a few dozen fighters. A simultaneous $1 billion covert program called Timber Sycamore conducted by the Central Intelligence Agency (CIA) aimed at fighting Syrian President Bashar al-Assad was more successful, but was decimated by Russian bombing, and canceled in mid-2017 by the Trump administration. The Obama administration began surveillance missions on Islamic State positions in Syria in September 2014. On 22 September 2014, the US, Bahrain, Jordan, Qatar, Saudi Arabia, and the United Arab Emirates (UAE) began to attack ISIL forces inside Syria, as well as the Khorasan group in the Idlib Governorate west of Aleppo, and the al-Nusra Front around Raqqa, as part of the international military intervention against ISIL.

Timber Sycamore and Syrian Train and Equip Program

At the direction of US President Barack Obama, the Central Intelligence Agency (CIA) was put in charge of operations worth about $1 billion annually to arm anti-government forces in Syria, an operation which formally began in 2013, more than two years after the start of the civil war in 2011. Prior to 2013, the CIA only supplied certain rebel groups of the Free Syrian Army with non-lethal aid, but later began providing training, funding, and intelligence to selected rebel commanders. Although a former intelligence adviser who spoke to journalist Seymour Hersh claimed the CIA had been facilitating the flow of arms from Libya to Syria in collaboration with "the UK [United Kingdom], Saudi Arabia and Qatar" since 2012 or 2011, the first confirmed CIA weapons arrived in Spring 2014: "There were just a handful, delivered to only one rebel group carefully vetted by the CIA". The group, Harakat Hazm, or the Steadfast Movement, showed off the new weapons system by posting the first successful strike on YouTube in April. Another of the groups being vetted was the Islamist Army of Mujahedeen, formed in January 2014 specifically to combat ISIL. However, there were indications that the Army of Mujahedeen was still being vetted in September 2014.

In addition to the covert CIA program, on 17 September 2014, the US House of Representatives voted to authorize the executive branch to overtly train and equip Syrian rebels against ISIL forces, at a cost of $500 million.

July 2014 rescue mission

Following the abduction of a number of foreigners in Syria, on 4 July 2014, the US carried out an operation to rescue foreign hostages being held by ISIL. US airstrikes were conducted against an ISIL military base known as the "Osama bin Laden Camp" while at the same time, two dozen US special forces soldiers dropped from helicopters near an ISIL-held building, thought to be for high-value prisoners. No prisoners were found in the building and the soldiers were quickly engaged by ISIL forces dispatched from Raqqa, which started a three-hour firefight. US forces concluded that the hostages were no longer at the site and abandoned the rescue attempt. At least five ISIL fighters were killed and one US soldier was wounded. Jordanian forces were also reportedly involved in the operation, with one Jordanian soldier reportedly wounded, but Jordanian involvement was not confirmed. Later on, it was reported that the hostages had been moved 24 hours before the attempted rescue. Following the mission, it remained unclear whether the operation failed due to bad intelligence or whether ISIL forces were alerted in advance of the mission.

In the aftermath of the rescue mission, and purportedly as a response to airstrikes in Iraq, ISIL beheaded three hostages over a one-month period: Americans James Foley and Steven Sotloff on 19 August and 2 September, respectively, and Briton David Haines on 13 September.

Surveillance flights over Syria On 26 August 2014, the US began conducting overt surveillance flights, including drones, over Syria to gather intelligence on ISIL targets, collecting information that would aid future airstrikes, even though airstrikes were not yet authorized at that point. No approval was sought from the Assad government for flights entering Syrian airspace.

US-led coalition against ISIL

In June 2014, the Iraqi government formally requested the United States to assist in its struggle against ISIL, following the group's offensive in northern Iraq that same month. Since then, the US led efforts to establish a global coalition to counter ISIL.

In response to this request, various sets of countries convened on 15 September and 3 December 2014, to discuss concerted action against ISIL. Present at all three meetings were the United States, United Kingdom, France, Germany, Italy, Canada, Turkey and Denmark.

The coalition of 5 September (10 countries) decided to support anti-ISIL forces in Iraq and Syria. On 10 September 2014, US president Barack Obama announced a "comprehensive" strategy to counter ISIL that "in concert with coalition partners [...] will defeat ISIL and deny them safe haven".