It was based on the book and adhered quite closely to it. But I can understand why someone who didn't read the book and didn't know what to expect, would be misled into thinking it was a war movie. It also featured Gibson and Weaver, who viewers generally associate with action-type films. As someone who has always been lukewarm about Gibson and who just watched this film last week, I found myself thoroughly surprised by how much I liked him in his role. This may very well be my favourite film of his.
You should watch him in:
Tim
The Bounty
Lethal Weapon
Blood Father
The River
Mrs. Soffel
Hamlet
The Man without a Face
Signs
Edge of Darkness
The Beaver