Thomas Paine opens the book with a general rant about the big decision that's facing all of America: the decision either to remain under British rule or to fight a war for independence. According to Paine, the entire world should want America to be free, since this will set an example for freedom and liberty that other countries could follow.
As the text unfolds, Paine lists all of the major problems with the British political system, especially the fact that they have rulers (kings and aristocrats) who inherit their power instead of gaining it through a democratic election.
For Paine, there is no path to freedom without democracy, and that's one of the main reasons that America needs to separate from the British.
Once he's laid out his opening points, Paine considers all of the arguments put forward by people who want to stay connected to Britain. One by one, he shoots these arguments down and shows that they are nothing more than excuses made up by cowards who don't want to put their lives on the line for freedom.
In the end, Paine takes aim at a group of religious pacifists known as Quakers and tells them they shouldn't be getting their religious views mixed up with American politics. In his closing lines, he asks all patriotic Americans to join him in mocking and despising anyone who would dare say that God condemns the America War for Independence.