The irony of political activism
To stake one's political believes on one's own well-being is ironic, because it is for that own person's well-being that one would hope for political reform. Moved for the community, Thoreau chooses to martyr himself by taking a stand against the government publicly, then refusing to pay the IRS, leading to his public arrest and public trial. The ironic sacrifice brought a lot of attention to the injustice of the Mexican War.
The irony of slavery
Slavery is another controversial issue during Thoreau's time, and in a way that seems ironic, because why should his views of the Mexican war have anything to do with his thoughts on slavery? The answer is that Thoreau knows that it is a similar kind of problem, because both the Mexican War and the history of American slavery have racism in common, thinking that someone might be worth less because of their race alone. In a word, the irony points to the insidious presence of white supremacy in US leadership.
The irony of the nightmare
In his dreams, Thoreau finds himself in unlikely horror, having to take a gun, being urged by a hoard of demonic voices to kill someone. The irony depicted is the human instinct toward violence. As he struggles to figure out what to do, he realizes that his emotions are deeper and more twisted than he can admit to openly. There is an ironic element of violence in him.
The irony of death
The novel points to death as an ironic element of Thoreau's political opinion. By considering death, he is able to find the courage to do what he feels is right, because although it seems to be counterintuitive to think this way, he can remember that in comparison with the sure fate of death, imprisonment, and insult are comparatively simple.
The irony of transcendentalism
Thoreau demonstrates a tendency toward transcendentalist thought in this novel. The irony is simply that, although interesting things do happen within the narrow frame of human life, it is in the sublime nature of all we take for granted that Thoreau finds his mind is finally at peace. He is poetic about transcendentalism, because he approaches the universe as if its magic can be exploited by skillful observation.
