THOSE who knew Iris Chang used to worry about how she could cope with the gloom of her chosen work. But when they visited the house in California that she shared with her husband and saw him playing with their two-year-old son by the swimming pool in the backyard, they were reassured.

The 36-year-old historian would sip lemonade with her friends at a Chinese café called the Tea House and, for a while, the torrent of terror that she frequently invited into her life would seem far away.

Were it not for the crinkled maps of China, the pictures of mass graves and the two desperately overstuffed Rolodexes on her desk, Chang might have been just another former high school homecoming queen from the aptly named Sunnyvale. But she had become one of the foremost young historians of her generation after publishing, seven years ago, a bestselling account of the Rape of Nanking, one of the worst episodes of human cruelty in recent history.

Her book brought international acclaim and controversy, and many spoke of a stellar future. It was not to be. In November she killed herself, no longer able to bear the weight of horrors from seven decades ago.

The Rape of Nanking in 1937 began with the march of invading Japanese soldiers up the Yangtse River. They occupied the Chinese capital of the time and soon conquest was followed by bloodlust. Soldiers slaughtered between 100,000 and 300,000 civilians sheltering in a few city blocks. Slowly.

Over a six-week period, up to 80,000 women were raped. But it wasn’t so much the sheer numbers as the details that shock — fathers forced at gunpoint to rape daughters, stakes driven through vaginas, women nailed to trees, tied-up prisoners used for bayonet practice, breasts sliced off the living, speed decapitation contests.

During the war the massacre was well known, but both Tokyo and Beijing preferred not to mention it over the four decades that followed.

Iris Chang was pitched into this maelstrom of history as a child when her immigrant parents, who had escaped from wartime China to the US, told their daughter how the Japanese “sliced babies not just in half but in thirds and fourths”. In the introduction to her book she wrote: “Throughout my childhood [the massacre] remained buried in the back of my mind as a metaphor for unspeakable evil.”

When, at 27, she read one of the few accounts of the atrocity still circulating in the West, she sensed a mission in life. “I was suddenly in a panic that this terrifying disrespect for death and dying, this reversion in human social evolution, would be reduced to a footnote of history, treated like a harmless glitch in a computer program that might or might not again cause a problem, unless someone forced the world to remember it.”

Chang soon made her first trip to China and sought out Sun Zhaiwei, a history professor in Nanjing, as Nanking is known today. “I provided her with an assistant and fixed appointments with some of the survivors,” he says. Chang was given free lodgings and unlimited access to archives on the tree-lined campus near where the Japanese breached the old city wall before beginning their slaughter.

When the book based on her research — The Rape of Nanking: The Forgotten Holocaust of World War II — was published two years later, it sold more than half a million copies and Chang became an instant celebrity in America. Hillary Clinton invited her to the White House and Stephen Ambrose, the doyen of US historians, described her as “maybe the best young historian we’ve got”.

She was also widely praised for the emotion and commitment she brought to her work. On book tours the slim, ponytailed author spoke with an intensity that few listeners expected. Many broke down by her side, feeling compelled to recount their own tales of horror even if these were unrelated to her subject.

Orphans, rape victims and Holocaust survivors all wanted to bare their souls to her, finally relieving themselves of agonies sometimes decades old. They felt encouraged by the passion that she brought to the sort of grievances few of them could tackle on their own.