From Civil Disobedience

During his stay at Walden Pond (later to become the subject of his published journal Walden, or Life in the Woods), Thoreau spent one night in jail for refusing to pay a poll tax meant to support America's war with Mexico. He composed a letter from jail that he would later integrate into Civil Disobedience, published in 1849 under the title Resistance to Civil Government. (It is interesting to note that the term "civil disobedience" does not appear in the actual essay.)