The right answer is: "How Thoreau protested". Since H.D. Thoreau was a young men, he could establish that something in his society, in his time, was wrong since the fact the people were divided in free and "legally slaves", the insurrection and death of a powerful leader reaffirmed his believes in a non-trustworthy government and not paying a voting tax represented for him the initial protest act.
Indeed, not only the introduction explicitly mentions the peaceful disobedience method of protesting, it also provides examples of famous proponents of this method, including Gandhi and Martin Luther King. The excerpt also implicitly contrasts peaceful protest with violent revolt, by mentioning not only Henry David Thoreau’s poll tax incarceration but also Nat Turner’s rebellion which are very dissimilar events. Nat Turner’s rebellion was a very violent slave uprising, where Nat turner and several slaves rebelled and massacred almost 100 white men, women and children while Thoreau’s incarceration hurt no-one and resulted in moral condemnation of the police.
