An injustice exists when history is only taught from one perspective. When it is accepted that there is only one right or wrong course for society. When money and a societal elite can control information. Education and awareness are the enemy of injustice. Howard Zinn tells the truth for people who sacrificed themselves and who fought battles without national holidays to celebrate them, medals, or monuments. His text is exactly what the title reveals: a People's History.
Injustices occur when a people's land is taken from them. When a government signs treaties with tribes and does not honor them. When a war is waged, both violently, culturally, and psychologically against a people. A government that denies its past and does not even try to adequately compensate the victims.
It is not justice to watch people starve, hungry children, when the government pays farmers not to grow food. People find a home on the streets while livable houses remain vacant. All occurs in the name of profit, well it is time for people to come before profit, that is just.