Columbus as a symbol of a bad hero
Columbus did an important thing, no doubt, but he also witnessed serious crimes against humanity and stood by while his own men raped and murdered innocent people. So why was he celebrated for so long as a true American hero? Columbus represents the effects of bad history—we end up praising people whose values were unethical, and Zinn feels that we should read all history with that skeptical awarenss.
The motif of political-economic corruption
Zinn's History shows the US Government to be susceptible to economic corruption. He doesn't analyze present situations until way later in the book, but he does analyze the Founding Fathers of America for their ethical motivation. He observes that, coincidentally, many of those politicians stood to earn a tremendous amount of money from Revolution.
The French involvement as a symbol
Also, Zinn observes that the US Revolution was mainly a French war against the English, but since the French Revolution followed behind the US Revolution, we forgot that, basically, we won because of the French. The fact that more people don't know that represents America's "America-centric" tendencies—it's an obvious bias, so the history isn't objective anymore.
The "War on Terrorism"
Simply put, Zinn uses the Bush administration's "War on Terrorism" as an archetype of injustice. Not only is it a war against a hypothetical concept, it mischaracterizes the motivations of the 9/11 hijackers, so that it looks like Muslims hate freedom or something. Then they invaded a country that has nothing to do with those attacks. He notices nefarious American activity in Saudi Arabia, Iraq, Palestine, and meanwhile—the "War on Terrorism" gave them enough public sway to do what they wanted in those places.
The unions as a symbol
Zinn challenges his readers to consider the history of American labor unions to be more central to their understanding of American life in general. He says that the labor unions, and the history of the growing industrialization of America—that they show a class division. He says that historically, American companies exploit their workers in every industry, because the people at the top are trying to get unimaginably wealthy, and the people at the bottom have to fight just for an honest wage. Zinn says this issue is one that we ignore at our peril.
