A schoolgirl, part of the generation of Cambodians who might use social media to make their nation more democratic. “Angkor Awakens” speaks to survivors of the Pol Pot regime and their descendants. (PhotoSynthesis Productions/Journeyman Pictures)

All wars have unintended consequences. One of the most devastating post-World War II examples was the genocide in Cambodia between 1975 and 1979. That small country’s extremist insurgents, the Khmer Rouge, led by Pol Pot, leapt into a leadership vacuum created by the war in neighboring Vietnam. What followed was a bloodbath.

Out of a population of slightly more than 7 million, the Khmer Rouge is estimated to have killed between 1.7 million and 2.2 million of their countrymen, targeting intellectuals first, and anyone else deemed disloyal.

Americans may know about this from the Oscar-winning 1984 film “The Killing Fields,” based on New York Times reporter Sydney Schanberg’s account of covering the conflict with his Cambodian interpreter, Dith Pran.

But it is the uncharted future of Cambodia, as much as the past, that concerns filmmaker Robert H. Lieberman in his intimate, deeply humane documentary “Angkor Awakens: A Portrait of Cambodia.” He talks to mostly English-speaking survivors of the genocide, their children and grandchildren. He talks to Cambodian and American scholars, to artists and politicians, and to former American diplomats who saw the disaster coming. He even got an interview with Prime Minister Hun Sen, Cambodia’s leader since 1985 who is often called a strongman.

Two young women and a young man laugh, citing a warning they say they have all heard, in some fashion, from elders who don’t otherwise speak of the killings: “If you don’t learn to do this or that and the Khmer Rouge come back, you will die.” They live in dread.

One woman warns that younger Cambodians, too, are “a very fragile generation,” although the equalizing power of social media has given them a sense of power.

“Angkor Awakens” looks back at the genocide in its first half, with somber interviews, grim archival footage of mass graves, artistic renderings and Cambodian-style shadow puppetry. The effect is always disturbing and occasionally graphic enough to make the PG-13 rating questionable.

Lieberman doesn’t look too far afield for American scholars, using academics from Cornell, where he’s on the physics faculty. But it is the Cambodian voices that give “Angkor Awakens” a welcome glimmer of light.

Near the end, a young woman says: “I feel we’re going somewhere better, but I don’t know how better.”

Unrated. At Landmark’s E Street Cinema. Contains footage, photos, artistic renderings and verbal descriptions of mass murder, torture, gravesites and human remains. In English and some Khmer with subtitles. 85 minutes.