Known at the time as "The Great War" and now as the first World War, it is somewhat ironic that much of the carnage was contained to a relatively small part of the globe (just don't tell that to the Belgians). This map comes from The World's Work: A History of Our Time (Volume xxxviii, Oct. 1919).
From the caption in the book:
The shaded area contains practically all the greatly devastated districts and ruined cities, with the exception of a few in Belgium such as Louvain, Verdun, Rheims, Cambrai, Arras, Lille, and many other cities and towns are centres of heavy destruction, while in a number of heavily shelled districts such as the Chemin des Dames and Ypres, every mark of human habitation is obliterated.It looks like about 1/3 of Belgium was laid waste and Parisians appear to be justified over any concern they might have held as the war was fought in their front yard. In the northwestern corner can be seen the Ardennes forest, and the names of many villages that would be an important part of the Battle of the Bulge in World War II including Bastogne, Stavelot and St. Vith.
I have added the blue lines to highlight national borders.