I completely agree that this story would not be as well understood if the reader did not have a prior knowledge of the treatment of Japanese people during the war. While I was researching the internment, I found many facts that I was unaware of and that changed my perspective on the story. I didn't know how long the Japanese were mistreated for, and I didn't know how horrible the conditions of the internment camps were.
I was fascinated to find out the Joy Kogawa was raised in an internment camp. Thank goodness she chose to share her experiences through writing so that those of us that weren't around at the time can understand the pain it caused.