The correct answer to this open question is the following.
Based on the paragraph, the primary structure used by the author is cause and effect.
This is an excerpt from the essay called "How We Entered World War I," written by Barbara Tuchman in April 1967. That year, the United States remembered the 50th aniversary of its participation in WorldWar 1.
Barbara W. Tuchman (1912-1989) was an American journalist that in 1943 worked in the US Office of War Information and wrote a book in 1960 called "The Guns of August," about the beginning of World War 1. She won the Pulitzer Prize with that book.