Everything Is Owed to Glory

France’s early-19th-century emperor was one of the most extraordinary men who ever lived: “What a novel my life has been!” he himself observed with complacency. It remains fiercely disputed, however, whether Bonaparte was an enlightened despot who laid the foundations of modern Europe or, instead, a megalomaniac who wrought greater misery than any man before the coming of Hitler.

Andrew Roberts, a British historian who has written widely and well about both statesmen and generals, is in no doubt of his own view. “Si...