Philip IV was in trouble. Spain’s far-flung empire, arguably the world’s most powerful, had seriously wobbled in the 1640s — and so had the king’s family life. When the bloody Thirty Years ...

Diego Velázquez’s “Queen Mariana of Austria” (1652-53), a monumental portrait of the daughter of the Hapsburg Emperor Ferdinand III, is at the Norton Simon Museum in Pasadena, Calif., ...