From the Document: "The conflict in Syria is entering its tenth year and has displaced roughly half of the country's pre-war population. As of 2021, five countries regularly operate in or maintain military forces in Syria: Russia, Turkey, Iran, Israel, and the United States--as well as transnational terrorist groups such as the Islamic State, Al Qaeda (AQ), and Lebanese Hezbollah. This piece provides a historical overview of the conflict."
CRS In Focus, IF11080
Congressional Research Service: https://crsreports.congress.gov/