Three of the books which I've read over and over since first encountering them in high school belong to Horne's classic trilogy on the Franco-Prussian Wars, the last two of which are better known by their official titles of World War I and World War II. I've spent most of my time with the latter two books, The Price of Glory: Verdun 1916 and To Lose A Battle: France 1940, because The Fall of Paris: The Siege and the Commune was out of print and damned hard to find in libraries, but all three of them are absolutely excellent pieces of writing. Horne has the gift that so many fiction writers think they have, that ability to weave dozens of minor characters into the flow of a story so that they illuminate the point that the author is trying to make; to a certain extent, his task is made easier by the nature of the Franco-Prussian Wars, which saw children in the first book becoming field officers in the second, and politicians or leaders in the final volume. This normally only happens in bad fiction, but when one recalls that the original Franco-Prussian War was fought in a relatively brief span of months between 1870-71, the First World War broke out just forty-three years later in 1914, and after that ended it was barely more than two decades before the Wehrmacht plunged into Poland to set off World War II, it seems entirely reasonable that Petain, Churchill, Gamelin and others might make appearances in all three books, if only peripherally.
The writing flows marvellously, never getting bogged down in pointless detail but at the same time covering all the important events. At the same time, Horne clearly has an eye for the macabre and piquant details of military and civilian life both. I can't recommend his books highly enough.