It ushered in the modern era of warfare, the mechanization of killing on a massive, industrial scale. It completely altered the international landscape, changing countries, shifting alliances and setting the stage for other wars and atrocities. And it was rather naively dubbed “the War to End All Wars.”

War or the threat of war has continued to darken the century that followed.

One hundred years ago this Sunday, on Nov. 11, 1918, the guns fell silent after the four bloodiest years in world history. When it was finally over, the First World War had claimed more than 8.5 million lives and left another 21.2 million crippled and forever scarred.

History tells us that the war’s proximate cause was the assassination of the Archduke Franz Ferdinand of Austria-Hungary. But that was only the spark that ignited a powder keg that had been allowed to accumulate for decades as the various Old World powers eyed one another with greed and suspicion, and as the leaders thumped the...