Story highlights New documentary tells story of Special Forces group that went into Afghanistan post-9/11 and overthrew Taliban regime

Peter Bergen says film raises serious questions about how much America is asking from these forces

Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of "United States of Jihad: Investigating America's Homegrown Terrorists." Bergen is a producer of CNN Films' "Legion of Brothers."

(CNN) The documentary feature film "Legion of Brothers" tells the stories of the handful of US Special Forces soldiers who, shortly after the 9/11 attacks, went into Taliban-controlled Afghanistan and within a matter of weeks overthrew the Taliban regime.

In the public's mind, Special Forces are often confused with the "door kickers" of Special Operations Forces -- such as SEAL Team 6 and Delta Force -- who are the United States' elite counterterrorism operators.

In fact, the primary mission of Special Forces, in particular the Army's Green Berets, who are profiled in the film, is to work "by, with and through" local forces on the ground to act as force multipliers. That means that Special Forces embed with local forces and work with them to achieve their common goals.

The Green Berets of US Special Forces 5th Group -- known as "the Legion" -- who led the anti-Taliban campaign represent a textbook case of a successful Special Forces campaign.

Five weeks after the 9/11 attacks, a 12-man Green Beret team led by Capt. Mark Nutsch was dropped into Afghanistan where they attached themselves to the army of the Uzbek warlord Gen. Abdul Rashid Dostum.

Read More