It is the only really serious book, which I have read by James Clavell. He was a prisoner of war in Changi, Singapore. His novel is a description of the way in which normal humanity can slip away in the face of overwhelming terror, stress, deprivation and cruelty. I found it quite sobering too.
Do you have to lose your humanity to survive in an extreme situation? I don't know the answer and I would hesitate to commit myself to an opinion on that one.
At any rate, I thought "King Rat" was a very moving and moral book.