I know. It's really funny how people seem to have a knowledge of history that begins solely with the colonization of the new world. They have zero recollection of the horrors of past civilizations. As if, somehow, the founders of the USA, are responsible for all evils in the world and everyone else was just getting along and hugging up until 1776.
And I recommend those people ask for a refund from their history teachers, because anyone who tells you history is black-and-white, good-and-evil, is selling you something. Humanity is one long stream of moral ambiguity. Any moral lessons derived from it are done by omitting contradictory evidence. A simple cruise through a Wikipedia article offers plenty of moral ambiguity--and that should be the minimum starting point for considering yourself knowledgeable in a subject.
Even the archtype of evil himself, Hitler, (and likewise Stalin with Russia) still managed to re-vitalize broken countries into industrial titans that we still benefit from today. Russia was literally a pre-industrial society before WW2. And it's interesting how people who believe in rigid good-guys/bad-guys have no problem driving a VW Beetle, or a Mitsubishi--they made the Kamakazi Zeros, by the way. And both companies benefited from slave labor. It's not even hidden knowledge:
http://www.nytimes.com/1996/11/07/world/volkswagen-s-history...
http://www.slate.com/blogs/the_slatest/2015/07/20/mitsubishi...