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.