Most of the time this phrase is associated with the Nazi genocide of WW2, in which six million Jews, and another six million other undesirables including gypsies, homosexuals, and Poles were systematically executed as a part of the "final solution".
It is important to remember this, no doubt. However, we should also not forget that this sort of dehumanization leading to mass slaughter is not unique. It's easy to say that it won't happen again, it can't happen again, especially if we can keep it distant and unique.
What I'd like to do in this thread is have people post historical events that you think it is important to remember, along with an explanation why they are important. I know I can't dictate what posters do, and there will have to be some political content, but I'd prefer that this be something more along the lines of a primer of historical events that still have some importance, or that you believe should have some importance, rather than have it devolve into a political debate of the issues involved in any individual event.
My contribution is the Ukranian famine of 1932-1933.
Short version: In 1932-1933, Soviet Russia systematically starved to death between 5 and 10 million Ukranians. They did this by setting grain quotas artificially high, confiscating grain supplies, destroying infrastructure, closing the borders to prevent food supplies from coming in, and confiscating aid sent from Europe and North America. At the same time, Russia was selling "surplus" grain to raise money for modernization. Between 15 and 30% of the Ukranian population died.
This was done primarily as punishment for resisting collectivism and attempting to retain a national identity. It's known as the Holodomor, and to a person of Ukranian descent is likely to evoke many of the same feelings as the Holocaust does for Jews.
Longer, more detailed version.
What do you want people never to forget? Remind us here.
Gilda