Sometimes you can learn something about today's world from a history book -- even a book about obscure characters in a long-ago time in a far-away corner of the planet, featuring conflicts between regimes that ceased existing at least a century ago. For me, one such book has been "Agents of Empire," by the Oxford historian Noel Malcolm, gaudily subtitled "Knights, Corsairs, Jesuits and Spies in the Sixteenth-Century Mediterranean World." The subjects of the book, members of two intermarried Albanian families, the Bruni and Bruti, filled all those roles in the years from 1560 to 1600. They started off in...