Syria Conflict Overview: 2011-2021
Updated August 3, 2023
Syria Conflict Overview: 2011-2021
Through 2021, conflict in Syria had persisted for a decade,
Figure 1. Syria
and had displaced approximately half of the country’s pre-
war population. This product provides a historical overview
of the conflict through 2021. As of 2023, five outside
countries regularly operate in or maintain military forces in
Syria: Russia, Turkey (Türkiye), Iran, Israel, and the United
States—as well as the U.S.-backed Syrian Democratic
Forces and transnational terrorist groups such as the Islamic
State, Al Qaeda (AQ), and Lebanese Hezbollah.
2011: Protests Emerge
In March, antigovernment protests broke out in Syria,
which has been ruled by the Asad family since 1971. Two
umbrella opposition groups emerged—one political, one
armed—with the leadership of both based primarily in
exile. Political groups established the Syrian National
Council (SNC), while military defectors formed the Free
Syrian Army (FSA), which claimed leadership over the
armed opposition but whose authority was generally
unrecognized by local armed groups. Escalating violence
Source: CRS, using ESRI, and U.S. State Department data.
prompted President Obama in August to call for President
regime; the United States, Turkey, and some European and
Bashar Asad to leave power. Meanwhile, the Islamic State
Arab Gulf states increased their support to the Syrian
of Iraq sent members to Syria to operate as a new group
opposition. U.S. allies differed in their goals and strategies,
called the Nusra Front.
and thus in their support for various opposition factions. ISI
2012: Insurgency
leader Abu Bakr al Baghdadi announced the merger of ISI
The conflict became increasingly violent, as Syria began to
and the Nusra Front into the Islamic State of Iraq and Al
use artillery and fixed wing aircraft against opposition
Sham (ISIS/ISIL). In August, a Syrian government attack in
targets. Extremist attacks became more frequent, and in
Ghouta using the nerve agent sarin killed an estimated
February the United States closed its embassy in Damascus,
1,400 people. President Obama requested congressional
citing security concerns. Armed groups began to seize
approval of a limited authorization for the use of military
territory throughout Syria, primarily in rural areas, while a
force to respond. Congress debated, but did not authorize
bombing in Damascus killed several senior regime officials.
the request. President Obama withdrew the request after
The United States and Russia signed the Geneva
Syria agreed to a joint U.S.-Russian proposal to join the
Communiqué, which called for the establishment of a
Chemical Weapons Convention, dispose of its declared
transitional governing body in Syria with full executive
chemical weapons stockpiles (completed in 2016) and
powers, and has been the basis of U.N.-sponsored talks
destroy declared production facilities (completed in 2018).
between the government and the opposition. Syria’s
2014: Operation Inherent Resolve Begins
political opposition settled into its present form as the
In February, Al Qaeda severed ties with ISIS. ISIS seized
National Coalition of Syrian Revolutionary and Opposition
vast stretches of territory in Syria and Iraq, and in June
Forces—aka the Syrian Opposition Coalition (SOC), or
declared a caliphate with its capital at Raqqah. The group
Etilaf in Arabic. The United States began non-lethal aid to
changed its name to the Islamic State (IS), and thousands of
bolster some opposition groups. In August, President
additional foreign fighters traveled to Syria and Iraq to join
Obama declared that the use of chemical weapons would be
its ranks. In July, the U.N. Security Council adopted
a “red line” for the United States.
Resolution 2165, authorizing cross-border aid into
2013: Proxy War, ISIS, Chemical Attacks opposition-held areas of Syria. In September, the United
In March, opposition forces seized the city of Raqqah.
States began air strikes against IS targets in Syria, pursuant
Subsequent opposition victories in the area led the
to the 2001 and 2002 Authorizations for Use of Military
government effectively to concede control of Syria’s rural
Force (AUMF); officials stated the Islamic State was a
northeast. Opposition victories prompted increased
direct derivative of Al Qaeda. A subsequent air campaign to
involvement by external allies of the Syrian government—
lift the IS siege on the town of Kobane brought the United
Lebanese Hezbollah, Iran, and Russia—to bolster the Asad
States into partnership with the Kurdish People’s
Protection Units (YPG). Also in September, Congress
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Syria Conflict Overview: 2011-2021
authorized a train and equip program for select Syrian
Syria conflict had “decisively shifted in the Syrian regime’s
forces. The program was designed to build new local force
favor.” In April, a chlorine gas attack by Syrian military
units capable of fighting the Islamic State, protecting
forces in Douma prompted British, French, and U.S.
opposition-held areas, and “promoting the conditions for a
missile strikes on three chemical weapon storage and
negotiated settlement to end the conflict in Syria.” In
research sites. By late 2018, the Syrian government had
October, the Defense Department established Combined
recaptured most areas formerly held by opposition forces.
Joint Task Force-Operation Inherent Resolve (CJTF-OIR)
2019: IS Defeat; Turkish “Safe Zone”
to formalize operations against IS forces in Iraq and Syria.
In March, SDF forces captured the final IS territorial
2015: Syria Train and Equip Begins
stronghold in Syria, and took custody of 12,000 IS
Opposition forces backed by Al Qaeda-linked militants
fighters—held in makeshift prisons—and over 60,000 IS
captured most of northwest Syria, IS fighters seized
family members—held in camps for internally displaced
territory in central Syria, and Kurdish fighters expanded
persons. Although a U.S. raid in October killed IS leader
their control along the Turkish border. In May, the United
Abu Bakr al Baghdadi, U.S. military officials warned that
States began training recruits for the Syria Train and Equip
the group was defeated but not eliminated, and described IS
Program. Russia began a military buildup in Syria, and
detainees as “one of the most significant risks to the success
started air strikes in September—targeting opposition
of the [defeat-ISIS] mission.” Separately, the Trump
groups and IS fighters. In October, U.S. Special Operations
Administration sought to end some aid for opposition-held
Forces deployed to Syria to support local partners as the
areas; Congress nevertheless appropriated funds for Syria
U.S. train and equip program shifted to support existing
programs and directed specific amounts for stabilization
vetted forces. Kurdish YPG forces aligned with a small
and other priorities. In October, Turkish-led forces began
number of non-Kurdish groups to form the Syrian
Operation Peace Spring, expelling U.S.-backed Kurdish
Democratic Forces (SDF), which began to receive U.S.
forces from areas of north-central Syria, which it termed a
support and would become the main local U.S. partner in
“safe zone.” President Trump withdrew U.S. forces from
the counter-IS campaign. Turkey opposed U.S. partnership
the area and repositioned some to the Eastern Syria Security
with the SDF because Turkey considers the YPG to be the
Area (ESSA).
Syrian offshoot of the Kurdistan Workers’ Party (PKK),
2020: Idlib Fighting; Russian Escalation
which both countries classify as a terrorist group.
The Syrian government escalated operations in Idlib, the
2016: Aleppo Battle; Turkey Strikes YPG last area still under the control of armed groups actively
In 2016, the U.S.-led counter-IS campaign successfully
seeking Asad’s removal. Fighting in Idlib between Syrian
severed most Islamic State access to the Turkish border—a
opposition groups (backed by Turkey) and Syrian
key supply and foreign fighter transit route. However, YPG
government forces (backed by Russia and Iran) resulted in
forces advanced along the border, raising Turkish fears that
the deaths of dozens of Turkish soldiers, possibly with
the YPG could permanently consolidate a contiguous area
Russian involvement. In March, Russia and Turkey signed
of control along the border. To prevent this, Turkey
a ceasefire agreement regarding Idlib. Outside the
launched Operation Euphrates Shield in northwest Syria
framework of Operation Inherent Resolve, the United States
along with allied Syrian opposition forces, targeting the
continued air strikes in Idlib against Al Qaeda-linked
YPG. Also, regime and opposition forces battled for control
forces operating in Syria. U.S. mechanized units deployed
of Aleppo—Syria’s largest city. In December, regime-
to northeast Syria to preserve U.S. freedom of movement
backed forces recaptured Aleppo in a battle the U.N.
following “an increase in Russian aggression.”
described as involving war crimes on all sides.
2021: IS Regroups; Siege of Daraa
2017: SDF Captures Most IS Territory
The Islamic State maintained a low-level insurgency in
Russia, Iran, and Turkey sponsored peace talks—known as
Syria and Iraq. U.S. military forces remained deployed in
the Astana Process—between Syrian government and
Syria, primarily in the ESSA but also at the At Tanf
opposition forces; U.S. officials described the talks as an
Garrison in the southeast. U.S. forces supported local
effort to circumvent ongoing U.N.-sponsored talks at
partners in their efforts to counter IS remnants. U.S.
Geneva. In April, a sarin gas attack by Syrian forces on the
officials assessed that without a U.S. presence, the SDF
town of Khan Sheikhoun killed an estimated 80-100 people.
would “likely seek protection from the Syrian regime to
In response, the United States launched missile strikes on a
protect it from a possible Turkish-backed offensive.” U.S.
Syrian military airfield. President Trump did not seek
military forces conducted airstrikes in June against facilities
congressional authorization prior to ordering the strikes, but
used by Iran-backed militia groups in the Iraq-Syria border
stated that he had acted “pursuant to my constitutional
region engaged in drone attacks against U.S. personnel and
authority to conduct foreign relations and as Commander in
facilities in Iraq. Residents in Daraa governorate boycotted
Chief and Chief Executive.” In October, SDF forces
the May presidential elections that resulted in Asad’s
captured the IS capital at Raqqah. U.S. officials announced
reelection for a fourth term. The Syrian government
that 2,000 U.S. personnel were operating in Syria.
isolated the city of Daraa until a Russian-brokered ceasefire
2018: Foreign States Escalate Operations in September. Idlib and other areas of northwest Syria
In January, Turkey and its Syrian opposition allies launched
remained outside of government control.
a second military operation in northwest Syria (Operation
Christopher M. Blanchard, Specialist in Middle Eastern
Olive Branch), targeting Kurdish forces and causing a
Affairs
manpower drain from SDF counter-IS operations in eastern
Syria. The U.S. intelligence community assessed that the
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Syria Conflict Overview: 2011-2021
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