The screenwriter, David Rabe, served in Vietnam. 'Casualties of War' was originally a New Yorker piece written by Daniel Lang. The movie's basis a 1969 article and later novel by Daniel Lang that documented a real incident in Vietnam. Would be interesting to know from whom Lang got the story on which he based the article.
Here's the Genghis Khan quote, made by Kerry in 1971, as reported by the Washington Times (May 2, 2004):
"He [Kerry] asserted our soldiers 'raped, cut off ears, cut off heads,... cut off limbs, randomly shot at civilians, razed villages... reminiscent of Genghis Khan, shot cattle and dogs for fun, poisoned food stocks, and generally ravaged the countryside.'"
The movie depicts rape (of a Vietnamese girl by American soldiers), razing villages, shooting for fun, etc. It also compares what the Americans were doing to the exploits of Genghis Khan.
Hmmm.