What war is going on in Number the Stars by Lois Lowry?

The central theme of Number the Stars is the difficulty of growing up. One could make the case that Lowry uses the context of World War II as a way of making these difficulties stand out clearly. The novel focuses on Annemarie Johansen's personal experiences with growing up, but her experiences are common to most young people. Growing up is presented as a struggle for identity. Does Annemarie belong to the world of adults or to the world of children? Such distinctions are always difficult to make, but the situations the war creates makes these distinctions even more difficult. The roles Annemarie must play blur the line between a child's responsibilities and an adult's responsibilities. Lowry uses the war to demonstrate how confusing the separation between childhood and adulthood can be. Because of the war, Annemarie needs greater protection, but at the same time has to learn things that one normally does not learn until later life.