In August of 1937, the Japanese army invaded China. By December 13th, they had defeated the Chinese army and invaded the nation's then-capital, Nanking. The events that followed, referred to as "the rape of Nanking," are documented in the film Nanking, showing at Sundance in the US Documentary competition. The structure of the film was put together largely through the journals and letters of a small group of missionaries, professors and doctors -- and a Nazi businessman, John Rabe -- who refused to evacuate the Nanking when the Japanese army invaded, choosing instead to band together to establish a "safe zone" within the city in order to protect the civilians who lived there.

Like Schindler's List and Hotel Rwanda, Nanking tells a tale of war-time horror through the story of people who tried to help. Directors Bill Guttentag and Dan Sturman (with a script co-written by Elizabeth Bentley) bring the events of the invasion of Nanking to life through vintage footage, interviews with survivors, and a staged reading of excerpts from journals and letters by a group of actors including Woody Harrelson, Mariel Hemingway, Rosalind Chao and Jurgen Prochnow. Through vintage footage we see Nanking as it was before the war -- a beautiful, park-like city with many Westerners living and working there. When the Japanese army invaded China, those Chinese civilians who could afford to flee Nanking left, knowing that the capital city would be a target, and all foreign occupants were ordered to evacuate. Shanghai fell on November 12, 1937, and a month later the Japanese army was in Nanking.

Prior to the physical occupation of the city, the Japanese army bombed Nanking relentlessly, turning much of the once-beautiful city to rubble; through vintage footage we see the Japanese bombs hitting the city, then the destruction they caused. The film then documents how, over the next six weeks, a small group of Westerners fought to protect the civilians against a brutal campaign of rape and murder. The Tokyo War Trials, which lasted from May 1946 to November, 1948, found that civilians of Nanking were buried alive, used for bayonet practice, and shot in mass groups. According to the Tokyo Trials findings, over 20,000 women and girls were systematically raped (and then often murdered) during the rampage.

Twenty-two Westerners stayed in Nanking to try to do something to help, and through their letters and journals we feel the moral dilemma they faced: They could get out and secure their own safety, but what about their Chinese friends and neighbors who couldn't leave? Who would protect them? German businessman Rabe (played in the film by Prochnow), Bob Wilson (Harrelson), an American surgeon who later testified at the Tokyo War Trials, and Minni Vautrin (Hemingway), the American headmistress of a missionary college, were among those Westerners who boldy established a two-square-mile safety zone, whose boundaries they had to fight daily to protect once the Japanese army invaded the city. Over 200,000 Nanking residents found safety within the border the group established. Although the Japanese troops did breach the zone, many lives were saved by this diverse group of Westerners banding together to save as many as they could, and this is as much their story as it is a docmentary about the attack on Nanking itself.

Nanking is a deeply affecting film. The scripted reading actually works more effectively than mere voiceover would have, bringing to life the people who were a part of the events that happened in Nanking during that time. War and violence are never pretty, and this is not an easy film to watch -- there is brutal and gruesome footage of the death and destruction that happened there.

The rape of Nanking remains a controversial subject in Japan, where some dispute that the events happened at all, or downplay their severity. As the seventieth anniversary of the rape of Nanking approaches, historians from both China and Japan are working together to, once and for all, attempt to reach agreement on what happened there. More films about Nanking are in the works, including one by a group of Japanese nationalists, tentatively titled The Truth About Nanking, that will dispute the Chinese version of what happened. Another film, titled The Rape of Nanking and based on the book by Iris Chang that inspired the production of this film, is being produced by the Chinese state media.

Nanking doesn't offer any easy answers -- and is it even possible to truly comprehend the mind-boggling evidence of humanity's capacity to cause hurt and suffering? In light of the current war in Iraq, you might say this is a political film as well; those who do not learn from history, they say, are doomed to repeat it, and Nanking -- along with the other war-based documentaries playing here at Sundance -- serves as yet another reminder than mankind still has much to learn.

(Full disclosure: Nanking was produced by AOL executive Ted Leonsis.)