Gilbert, Martin: The First World War, a complete history (Henry Holt and Company, inc. New York, New York, 1994).
Personal Comments- Before I begin, let me say that a clear understanding of the motives behind World War II requires at least a broad comprehension of the causes and outcomes of World War I. It is with this perspective that I suggest finding a decent book on the "Great War".
Martin Gilbert's book is an average accounting written with barely sufficient documentation. This is not normally a concern of mine, since most books I have read have been so well documented from primary sources, but this is merely a condensation of other books. To cite books such as "Battlefields of the 20th Century", which in turn cites other books, which finally cite primary sources, is abysmal. A well written, historical book of a topic as recent as World War I (relatively speaking) should go back to original maps, letters, and interviews.
Having said that, this book was a good refresher for what I learned about World War I from a class I took in college. As an introduction to the First World War as a whole it is sufficient, but any serious researcher will thirst for more.
Winter, J.M.: The Experience of World War I (Oxford University Press, New York, New York, 1988).
Personal comments- This is the book that was used as a textbook for a class I took in college on World War I. It is similar to the American Heritage series on wars, with pages full of text, maps, and pictures. It is organized in a very interesting way. Instead of a strictly chronological organization, it is subdivided into catagories such as "the politicians' war", "the generals' war", "the soldiers' war", and "the civilians war". Each of these four catagories is divided into chronological sections. By approaching the war in this manner, Winter allows the reader to individually look at the decisions and experiences of all levels of those involved individually.