warning for mentions of genocide 

from chapter one of History is a Weapon: A People’s History of the United States by Howard Zinn; emphasis mine

One can lie outright about the past. Or one can omit facts which might lead to unacceptable conclusions. …

Outright lying or quiet omission takes the risk of discovery which, when made, might arouse the reader to rebel against the writer. To state the facts, however, and then to bury them in a mass of other information is to say to the reader with a certain infectious calm: yes, mass murder took place, but it’s not that important-it should weigh very little in our final judgments; it should affect very little what we do in the world. …

My argument cannot be against selection, simplification, emphasis, which are inevitable for both cartographers and historians. But the map-maker’s distortion is a technical necessity for a common purpose shared by all people who need maps. The historian’s distortion is more than technical, it is ideological; it is released into a world of contending interests, where any chosen emphasis supports (whether the historian means to or not) some kind of interest, whether economic or political or racial or national or sexual.

Furthermore, this ideological interest is not openly expressed in the way a mapmaker’s technical interest is obvious (“This is a Mercator projection for long-range navigation-for short-range, you’d better use a different projection”). No, it is presented as if all readers of history had a common interest which historians serve to the best of their ability. This is not intentional deception; the historian has been trained in a society in which education and knowledge are put forward as technical problems of excellence and not as tools for contending social classes, races, nations.

To emphasize the heroism of Columbus and his successors as navigators and discoverers, and to de-emphasize their genocide, is not a technical necessity but an ideological choice. It serves- unwittingly-to justify what was done. My point is not that we must, in telling history, accuse, judge, condemn Columbus in absentia. It is too late for that; it would be a useless scholarly exercise in morality. But the easy acceptance of atrocities as a deplorable but necessary price to pay for progress (Hiroshima and Vietnam, to save Western civilization; Kronstadt and Hungary, to save socialism; nuclear proliferation, to save us all)-that is still with us. One reason these atrocities are still with us is that we have learned to bury them in a mass of other facts, as radioactive wastes are buried in containers in the earth. We have learned to give them exactly the same proportion of attention that teachers and writers often give them in the most respectable of classrooms and textbooks. This learned sense of moral proportion, coming from the apparent objectivity of the scholar, is accepted more easily than when it comes from politicians at press conferences. It is therefore more deadly.