From the story here:
Millions of people were persecuted, publicly humiliated, beaten or killed during the upheaval, as zealous factionalism metastasized countrywide, tearing apart Chinese society at a most basic level. ... The Cultural Revolution is considered to have begun May 16, 1966, when the Communist Party's Politburo purged a number of leading officials. Over the following decade, Mao deposed two heirs apparent, his "Little Red Book" of sayings was elevated to the level of holy scripture, and millions were imprisoned, sent to labor camps or exiled from the cities.
