Somebody: However, Diamond does deal with non-European examples of conquest compelled by the same materialist determinants (like disease immunity, agriculture, and technology). For example, the farming/herding Bantu-speaking people of Africa did not carry with them a Greco-Roman cultural ancestry, but they nonetheless overwhelmed the hunter-gathering Khoisan, until the latter were restricted to the Southern end of the continent. The same forces at work in the American example, the fact that the Bantu made use of iron and were farmers, allowed them to displace Khoisan Africans. He deals with some other examples of well: of Chinese displacing Austronesians and of Polynesians taking over from Melanesians.
Still, I don't want to dismiss the importance of the Greco-Roman heritage in the European conquest of the Americas. You don't have Cortez and Pizarro without Alexander and Julius Caesar. But I think it's difficult to claim that they introduced conquest as such to mankind. I suspect after archaeology and anthropology have had their final word, it will be apparent that the first conquests of Homo sapiens were of our archaic kin the Neanderthals and other primitive Homo, who they both displaced and intermixed with (if the latest genetic evidence is accurate).