During a discussion at the Brookings Institution last week on identifying emerging security threats, CIA Director John Brennan said the bedlam in Syria has become one of the most intricate issues the US faces.

“I must say in my experience in working in Middle Eastern issues, Syria is the most complex, complicated issue I have ever had to deal with,” Brennan said in a question-and-answer session.

Brennan, who has been at the helm of the CIA since 2013, said Syria’s chaos has resulted from “so many internal players, so many external players, so many goals and objectives that are frequently in tension with one another.”

Syria’s civil war has been ongoing since March 2011 and features a bevy of competing groups, often backed by international actors. The Syrian government is currently supported directly and indirectly by both Russian and Iran, while the US and other Middle Eastern nations support various rebel forces to at least some extent.

Russia has carried out airstrikes against ISIS and other rebel groups throughout the country since September 2015. And Iran has bolstered the Assad regime by deploying Shiite militias in the country, by sending Afghan refugees into the country to fight, and by encouraging the Lebanese terror group Hezbollah to come to the aid of the Syrian government.

Arrayed against the Syrian government are a plethora of rebel groups with various ideologies, foreign backers, and their own alliance networks. The number and fluidity of the groups has caused headaches for their various international backers — such as the US, France, Turkey, and the Gulf states — especially as even US-vetted groups are believed by Amnesty International to have committed war crimes.

One of the strongest rebel forces on the ground is the Nusra Front, Al Qaeda’s affiliate in Syria, which fights alongside certain segments of the Syrian opposition. And the Nusra Front has become enough of a concern for foreign powers that Russia and the US have agreed to start coordinating their airstrikes to better destroy both Nusra and ISIS.

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