The Syrian government is led by President Bashar al-Assad, who came to power by suceeding his father in 2000. During his rule, Syria has been criticized for human rights abuses, the executions of citizens and political prisoners, and censorship.
The government is supported by Russia, Iran and the Lebanese militia Hezbollah.
In 2019, forces loyal to Assad have managed to reclaim most of Syria once held by the opposition with the help of Russian airstrikes.
ISIS is a militant group that attracted global attention in early 2014 when it released videos of executions of soldiers and civilians, including journalists and humanitarian workers.
It has been designated as a terrorist organisation by the United Nations as well as by many countries, including the United States.
In 2019, the group has virtually lost all of its territory in Syria and Iraq. Its leader, Abu Bakr al-Baghdadi, was killed during a raid in Syria's Idlib province conducted by U.S. special forces in October.
The Syrian Democratic Forces is a coalition of multi-ethnic fighters in northeastern Syria led by the Kurdish-militia People's Protection Units. It is one of the most effective fighting forces against ISIS.
Backed by U.S. air support, the SDF took control of Raqqa, the capital of ISIS, in October 2017.
The SDF is supported by United States. However, it is seen by Turkey as an extension of the Kurdistan Workers' Party, a militant insurgent group fighting the Turkish government since the 1980s.
In October 2019, the Turkish Armed Forces along with the Turkish-backed Free Syrian Army launched a military offensive against the SDF, following an announcement by President Trump to withdraw U.S. troops from northern Syria.
Hay'at Tahrir al-Sham is a jihadist group formed in 2017 by the merger of several Islamist groups. Al-Qaeda's branch in Syria, Al-Nusra Front (aka Jabhat al-Nusra), is one of the prominent groups that merged into Hay'at Tahrir al-Sham.
Hay'at Tahrir al-Sham is the dominant group in rebel-held Idlib province, prompting smaller and moderate rebel groups to coorperate with it in the fight against the Syrian government.
It has been designated as a terrorist organization by the United States, Canada, and Turkey.
The Syrian opposition, sometimes referred to as Syrian rebels, is a collection of anti-government groups seeking to overthrow the government of President Bashar al-Assad.
It is supported by the United States and its allies, Saudi Arabia and Gulf countries, and Turkey.
In 2014, the United States and a number of countries established the Combined Joint Task Force – Operation Inherent Resolve (CJTF–OIR) with the aim of combatting ISIS. Countries that have conducted airstrikes against ISIS include the United States, Australia, Bahrain, Canada, France, Jordan, the Netherlands, Saudi Arabia, Turkey, the United Arab Emirates, and the United Kingdom.
The United States has also supplied advisors, weapons, training, and supplies to the Syrian Democratic Forces in their fight against ISIS.
In April 2019, a joint investigation by Amnesty International and Airwars reported at 1,600 civilians were killed by coalition airstrikes and U.S. artillery shelling during the battle to capture the Syrian city of Raqqa from ISIS in 2017.
The Russian Air Force began conducting airstrikes in Syria in support of government forces in September 2015. The strikes were conducting using the Khmeimim Air Base in Latakia Governorate, and they targeted Syrian opposition groups and ISIS.
Russian intervention has enabled significant gains for the Syrian government, including the recapture of Palmyra from ISIS and securing control over Aleppo city from opposition groups.
Russian Military Police and special forces continue to patrol areas control by government forces and support government operations against opposition groups in Idlib province.
Iran has provided billions of dollars of military aid, and logistical and technical support for the Syrian government.
The Iranian Revoluntionary Guard Corps, a branch of the Iranian Armed Forces, has funded, trained, and equipped the Afghan Shia militia Liwa Fatemiyoun and the Pakistanis Shia milita Liwa Zainebiyoun fighting in Syria alongside pro-government forces.