Lives don't often provide the satisfying arc we appreciate in fiction - Unbroken does. The first third is an adventure, the middle half is sheer torment, and the end is redemptive.
In 1936 Louie Zamperini was an Olympic distance-runner, drafted before he could fulfill his dream of winning the 1500 meters in 1940. He served in the Army Air Corps in the Pacific theater in WWII, escaped the wreckage when his plane crashed in the ocean, and spent over 40 days in a raft, living by ingenuity and luck amid sharks, on what meager food and water they could capture from sea and sky, only to land emaciated on a Japanese-occupied island where he and his surviving crew member were taken prisoner. He spent the next two horrific years interned first in a secret interrogation camp then in two notorious POW camps where he endured unimaginable torments at the hands of cruel men.
The rebuilding of Japan into an ally against the communist countries of Asia required the US to turn a blind eye to Japanese wartime abuses, so it is a revelation for anyone younger than the generation who fought them, to read about the deliberate starvation, ghastly medical experiments and calculated barbarities that claimed the lives of many POWs and twisted the post-war existence of the rest. From our comfortable distance of hindsight we decry the use of the atomic bombs dropped on Hiroshima and Nagasaki, but this story bolsters the contention of members of the war generation, that use of this shocking new weapon was the only thing that prevented a full-scale invasion of Japan, to end that war.
During the castaway section, when one of the ever-present circling sharks leaps from the water attempting to grip "Zamp" in its maw, we feel a thrill - what an adventure, what a feat of survival. But when after many days in their small raft, starving, the men are spotted by a plane (rescue! at last!) then that plane strafes them, passes, and returns to strafe again, the reader feels jolted by the world's injustice. And that's only the beginning, the first step into their long hell.
Incarceration is a terrible ordeal, gripping and appalling, and Hillenbrand tells it vividly - the men's starvation, illness and thirst, the small measures of defiance that bring on added punishments but keep their wills alive, the whole twisted world of prison camp commanders and staff in which the POWs' rations are sold off on the black market while the dregs of the military wield absolute control. These men's experience is more Holocaust than The Great Escape.
But we, like Zamperini, do finally achieve peace. Barbarity wasn't invented in the wars being fought now - it is as old as human altercation. This book is as powerful an argument in favor of diplomacy and peace, as you could find. War is not a heroic enterprise, War is Hell. We do well to remember that when we clamor for vengeance, for matching destruction by "our enemies" with our own.