The media
In Anderson's treatment of nationalism, he suggests that there are Imagined Communities that people participate in by accepting myths about their own life and its connection to other narratives, like the history of the US government, for instance. The media is an ironic part of the problem, because people who run media organizations can exploit these belief patterns for money. The process is simple: reinforce the narrative that many people believe, ensure audience, collect ad revenue.
The constructed narrative
The irony of nationalism itself is that to the people who believe the myth, it isn't a myth at all. It is their real life. But it is a myth, because there is a narrative about one's participation in a system (typically the system is 'us against them'), and people without strong social attachments can easily supplement their identity by participating in these narratives through strongly-held (one might say religious) belief. The irony is that some of the strongest social forces are the narratives people construct.
Capitalism and nationalism
There is an ironic feedback loop between a free market and a nationalistic identity. Although they seem completely disconnected, they are not. A person with a strong sense for what is American (for instance) can easily start to believe that what it means to be "American" is to buy the things an American should buy. One can see that businesses thrive off of people who feel an emotional attachment to celebrating their identity in this way.
Inadvertent civics
To understand one's place in history and to be alert to the reality of one's own government and economy is called "civics," and Anderson's book shows that this civic aspect of human life has been changing. Because of nationalism and its myths, a person can begin to have an ironically antithetical point of view on civics. This happens when a person accepts the narratives about national citizenship that circumvent their need to fix problems that exist. To put this plainly, if a person doesn't do the hard work of understanding the question of a place in history, someone can come along and fill in the gaps—typically through the media.
Belief and truth
The book is underscoring an important dilemma between how the world seems and how the world is. To accept beliefs about one's identity for emotional reasons has dangerous effects on a person's ability to discern truth, because they stake their identity on constructs that will have to be abandoned if truth is to be discerned. For example, it is extremely challenging to show someone that their point of view is too dependent on a certain political agenda, because they are committed to the agenda for emotional reasons—with only enough reason to defend the attachment. Political belief is shown to be the ironic enemy of truth and reason.
