The actress was speaking exclusively to the BBC before the screening of First They Killed My Father, a true-life account of the Khmer Rouge genocide through the eyes of a child.
She said she hoped the film, which she directed, would help Cambodians to speak more openly about the trauma of the period.
Two million people died.
Jolie, now a UN refugee agency special envoy, first visited Cambodia for the filming of 2001 hit Lara Croft: Tomb Raider.
She later adopted Maddox, her oldest son, from Cambodia.