Final answer:
Thoreau advocated for the abolition of slavery in America through civil disobedience and nonviolent resistance to unjust authority.
Step-by-step explanation:
According to Henry David Thoreau, a man should abolish slavery in America by practicing civil disobedience and resisting authority when it is unjust. Thoreau argued that individuals have the right to refuse allegiance to, and resist, the government when tyranny or inefficiency become unendurable. His philosophy on civil disobedience influenced notable figures like Leo Tolstoy, Mohandas Gandhi, and Martin Luther King, Jr. Thoreau's stance involved standing by his principles, living a simple life, and defying unjust laws through nonviolent methods. He demonstrated this through his refusal to pay poll taxes that supported slavery and the Mexican-American War, which led to his brief imprisonment.