What is the theme in Vanity Fair by William Makepeace Thackeray?

There is one clear, overarching theme in Vanity Fair: A Novel without a Hero, and Thackeray telegraphs it in his title and subtitle. In the pages of Vanity Fair, all is vanity and all are vain. Some are more vain—more obsessed with self and with the ephemeral treasures of social position and money—than others, but none, in the author's estimation, can be called heroic.