In Aztec and colonial Central Mexico, every individual was destined for lifelong placement in a legally defined social stratum or estate. Social mobility became possible after independence from Spain in 1821 and increased after the 1910-1920 Revolution. By 2000, the landed aristocracy that was for long Mexico's ruling class had been replaced by a plutocracy whose wealth derives from manufacturing, commerce, and finance--but rapid growth of the urban lower classes reveals the failure of the Mexican Revolution and subsequent agrarian reform to produce a middle-class majority. These...