The Romans committed genocide often enough.
They completely wiped out Carthage as a nation, destroying the city, navy, army, culture, everything.
They also committed genocides in Iberia, Gaul, Italy (Alba Longa if I remember correctly), Asia Minor, Middle East. It's just that it was so common that it wasn't recorded as a horrible event, just a way to win.

Genocide hasn't really come to the fore because there was a de-humanization element by the victors, so that when the Americans wiped out American-Indians, it was destroying a savage killer, not a human being.

I would say that genocide should not be permitted, ever.

I would like to say that the Holocaust wasn't a major reason for U.S. involvement. It was not widely known, and had it been known, there were people who supported the idea. Eugenics and breeding a superior race, before there was a concept of genetics or DNA.

I think that in modern society, genocide should not be allowed or tolerated.

I would also like to ask about the Armenian genocide. I'm sorry to the Turks here, but why isn't there anything about it, when it did occur?