Because the novel is set during World War II and is intrinsically connected to the war, historical allusions play a major role in the book.
Historical allusions: In Chapter 2, Finny discusses the bombing of Central Europe with the professors and their wives (26). Similarly, when Finny creates his own game in the same chapter, he decides to name it "blitzball" (37) in connection with the Blitzkrieg (Germany's lightning-fast invasion of Poland). Later in Chapter 7, Brinker teases Quackenbush about "Mussolini's" army, being a "kraut" (German), and Pearl Harbor (all references to America's WWII enemies or attacks--98). In Chapter 8, as Finny rants about the stupidity of enlisting (because he can no longer enlist), he mentions Madame Chiang Kai-shek and the Yellow Peril (references to China and the leaders of what would eventually be Taiwan--109). In a similar discussion about the war, Finny tells Gene that the "fat old men" are just making up the war to keep the younger generation from taking their jobs. He is referencing stock market gurus and other wealthy tycoons who made money from WWII industry (115).
Knowles includes other historical allusions and literary ones (when he discusses the classes/subjects that the boys study).