Ultimately, what moral question does zinn raise for historians to consider?

What he asks is whether all the bloodshed and deceit from Columbus to Cortes, Pizarro, the Puritans-a necessity for the human race to progress from savagery to civilization.

Basically, he wonders whether it was really necessary to commit all the monstrosities that happened in the history of the "civilized" world on the road to civilization, or was it possible to become developed and civilized without it.