Thoreau was also a passionate advocate for individual conscience against unjust authority. His essay Civil Disobedience (1849), written after spending a night in jail for refusing to pay taxes that supported slavery and the Mexican-American War, argued that citizens must not allow governments to overrule their moral judgment. This work profoundly influenced later leaders such as Mahatma Gandhi and Martin Luther King Jr.
His other notable works include A Week on the Concord and Merrimack Rivers (1849), Cape Cod (1865), and his extensive journals, admired for their keen observations of the natural world. Thoreau died of tuberculosis in 1862, leaving an enduring legacy in literature, philosophy, and environmentalism.