I liked "Code Talkers" personally. I got it for my 12 year old son (who hasn't yet read it), but honestly, it is a book that could be read in one sitting by an advanced reader of that age (ie, not a difficult book). It is light on factual information about the war, but rich in insights into the Navaho culture and their role in the war, how they were treated, how they preserved their traditions in a hostile environment, etc- so there is certainly an angle of social justice, just not the typical one.
Other relevant books our kids have enjoyed include "The Boy in the Striped Pajamas," "Number the Stars" and "The Book Thief". I'm sure there are several others, I will add them if they come to mind.
