George Brown Tindall and David E. Shi, eds., America: A Narrative History, 5th ed., vol. 1 (New York: W. W. Norton and Company, 1999), 551-552.
While Thoreau was at Walden Pond, the Mexican War erupted. Believing it an unjust war to advance the cause of slavery, he refused to pay his state poll tax as a gesture of opposition, for which he was put in jail (for only one night; an aunt paid the tax). The incident was so trivial as to be almost comic, but out of it grew the classic essay "Civil Disobedience" (1849), which was later to influence the passive-resistance movements of Mahatma Gandhi in India and Martin Luther King, Jr., in the American South.