Thoreau refused to pay his poll tax as a protest against slavery and the Mexican-American War, spent a night in jail, and wrote this essay about it. The argument is radical: individuals have not just the right but the duty to resist unjust governments. Gandhi read it in a South African jail; Martin Luther King Jr. read it in college. The prose is characteristically dense and aphoristic. The influence on nonviolent resistance movements worldwide has been incalculable. One night in jail became a philosophy of revolution.