You be the author. What would you put in a textbook on the First World War?

Students have been hired to write a chapter on the First World War for a high school history book. The publisher, however, has put them on a tight budget for the number of pages and illustrations. Students, taking the roles of historians and authors, must choose only the three most important events of the time.  They are responsible for researching the events of the First World War and writing a letter to the textbook publisher outlining and defending their choice of events. Students must use the criteria for historical significance when making their argument.