Short answers, pulled from the story.
Democracy in America is a two-volume French work analyzing why republican representative democracy succeeded in the United States while failing in many other countries. Tocqueville examines American religious, political, and social life to identify the conditions that sustain democratic self-government, including the role of mores, religion, voluntary associations, and local governance.
The first volume was published in Paris in 1835 and the second in 1840. Both volumes were immediately popular in Europe and the United States.
In 1831, the French government sent Tocqueville and Gustave de Beaumont to study the American prison system. Tocqueville later acknowledged in letters that the prison study was a pretext, and the two spent nine months traveling the country to study American society, religion, politics, and economic life.
Tocqueville anticipated the violent conflict over slavery that would lead to the American Civil War and foresaw a superpower rivalry between the United States and Russia, which materialized as the Cold War after World War II. He also warned that industrial ownership of labor could produce a new form of aristocracy capable of dominating democratic society.
Tocqueville used the phrase to describe a risk specific to democratic societies: that majority opinion could suppress dissent and nonconformity through social pressure rather than through formal law. He saw this as a distinct threat to individual freedom that did not require any official act of censorship.
The Tocqueville effect is the observation, drawn from Democracy in America, that social frustration tends to increase as social conditions improve. Tocqueville argued that as inequality decreases, people become more resentful of the privileges that remain, which leads them to demand greater state intervention to eliminate those remaining distinctions.