man's inhumanity to man

I am currently reading "Unbroken" by Laura Hillenbrand. It is the true story of an Olympic runner, Louie, who served as a bombadier in World War II.

His plane crashed and he survived 41 days on a 2-man life raft with no provisions. Then he was captured by the Japanese and imprisoned as a POW. He served time at a couple different POW camps for a total of 2 1/2 years.

The story is fascinating but I am utterly appalled at the treatment that he and the other POWs received at the hands of brutal guards. Not all of the guards were brutal but those that were mean were beastly. Some of the guards seemed to find great pleasure in beating the prisoners. At one point, Louie was punched in the face 220 times (losing consciousness several times only to be revived and punched again). At another point, Louie was hit in the temple with a huge belt buckle repeatedly. He'd have his face rubbed in excrement. The inhumanity goes on and on.

On top of that, the Japanese never gave the POWs the Red Cross provisions but kept them for themselves or sold them. They literally starved the prisoners. Louie's weight dropped below 80 pounds at one point. How does a grown man, an athlete at that, survive at 80 pounds? Over 37 percent of American POWs interred in Japan died. The Japanese completely ignored Geneva convention rules for treatment of prisoners.

I have such a hard time believing that even in times of war people can be so callous to their fellow men.

What makes a person forget that a prisoner is a human being first and foremost and an enemy second?