Thoreau's Civil Disobedience espouses the need to prioritize one's conscience over the dictates of laws. It criticizes American social institutions and policies, most prominently slavery and the Mexican-American War.
Thoreau begins his essay by arguing that government rarely proves itself useful and that it derives its power from the majority because they are the strongest group, not because they hold the most legitimate viewpoint. He contends that people's first obligation is to do what they believe is right and not to follow the law dictated by the majority. When a government is unjust, people should refuse to follow the law and distance themselves from the government in general. A person is not obligated to devote his life to eliminating evils from the world, but he is obligated not to participate in such evils. This includes not being a member of an unjust institution (like the government). Thoreau further argues that the United States fits his criteria for an unjust government, given its support of slavery and its practice of aggressive war.
Thoreau doubts the effectiveness of reform within the government, and he argues that voting and petitioning for change achieves little. He presents his own experiences as a model for how to relate to an unjust government: In protest of slavery, Thoreau refused to pay taxes and spent a night in jail. But, more generally, he ideologically dissociated himself from the government, "washing his hands" of it and refusing to participate in his institutions. According to Thoreau, this form of protest was preferable to advocating for reform from within government; he asserts that one cannot see government for what it is when one is working within it.
Civil Disobedience covers several topics, and Thoreau intersperses poetry and social commentary throughout. For purposes of clarity and readability, the essay has been divided into three sections here, though Thoreau himself made no such divisions.