The theme probably shouldn’t simply be "warfare" but World War II specifically. The members of the Secret Annex follow the war news religiously via radio broadcasts. There are daily reminders that the country is at war, right down to the food that is available. Everybody’s life is in constant danger.
Although Anne’s adolescence is spent in hiding, her response to other people is remarkably similar to the way teenagers living normal lives in times of peace respond.
Because Anne’s early teen years are spent in hiding, her experiences, emotions, and reactions to people are markedly different than those of a teenager living in a time of peace.