The film begins with the idea that 25 percent of the people in the world who are incarcerated are incarcerated in the U.S. Although the U.S. has just 5% of the world's population. "13th" charts the explosive growth in America's prison population; in 1970, there were about 200,000 prisoners; today, the prison population is more than 2 million. The documentary touches on chattel slavery; D. W. Griffith's film "The Birth of a Nation"; Emmett Till; the civil rights movement; the Civil Rights Act of 1964; Richard M. Nixon; and Ronald Reagan's declaration of the war on drugs and much more.