On the Eastern Front, the German army was imploding under the weight of 5 million advancing infantrymen of Russia's Red Army. At the same time, Allied four-engine bombers, with superb long-range fighter escorts, at last were beginning to destroy German transportation and fuel infrastructure. Yet Hitler held off for another 11 bloody months. Why?

Have the United States and Europe simply run out of steam?

Leon Trotsky's brutal assassination by a Stalinist agent in Mexico in August 1940 might seem an unlikely wellspring for fiction, but it has inspired more than one novelist in recent years. Barbara Kingsolver's "The Lacuna," published in 2009, centered on an aspiring writer, a Mexican-American, who is shown joining Trotsky's Mexican household as it braces for the Kremlin's assault. In the same year, in Spanish, Leonardo Padura's "The Man Who Loved Dogs" was published, making its central figure the real-life assassin himself, Ramón Mercader. That novel is just now appearing in an English translation, alongside, coincidentally, John Davidson's Trotsky-themed "The Obedient Assassin."

May 8 marked the end of World War II in Europe 70 years ago -- a horrific conflict that is still fought over by historians. More than 60...