"The book takes place around World War II, when a group of young boys are stranded on a deserted island. They struggle to survive, find rescue, and stay civilized, all while fighting their primal urges which are threatening to take control."
That would be my suggestion.
However, the first sentence now seems rather abrupt and it seems to imply that the story is true.
So try...
"The book takes place is set around the time of World War II, when a and involves a group of young boys who are stranded on a deserted island. They struggle to survive, find rescue, and stay civilized, all while fighting their primal urges which are threatening to take control."
Granted, this is probably too late.
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