In my view, the key events that shaped the 20th Century, and even our world today occurred in the First World War. One of my wife’s colleagues asked her to recommend a book about WWI, and she in turn asked me. I suggested “The Guns of August”, a rather obvious place to begin, and mentioned “Goodby to All That” and “All Quite on the Western Front”. Barbara Tuchman’s book turned out to be a revelation.
I agree. World War I is still biting us in the butt today. Virtually all,of the Middle East problems date from then, the rise of the USSR and communism, the destruction of a whole European generation, the list of consequences can go on and on.
Another good World War I read is August 1914 by Solzhenitsyn.