In this quote, Arendt identifies the origin of racism (as opposed to earlier race-thinking) with the imperialist period of European history beginning in the nineteenth century. Before this, she asserts, racial (or racist) thinking was mere opinion rather than ideology. In the contact between the Boers in South Africa and the indigenous peoples there, the Boers (who represented the marginalized elements of Dutch and European society transplanted to South Africa) wished to set themselves up as masters and self-proclaimed gods over the Africans. This is an instance, or perhaps the archetypal action, illustrating the quote in which she describes race as an "emergency explanation," a rationalized or pseudo-rational process Europeans devised to keep themselves separated from others.
Arendt's focus upon the imperialist period of the nineteenth and early twentieth centuries appears to be the cause of this specialized definition and explanation of racism. One wonders why the entrenched racial thinking that has been in evidence throughout the history of the American continent from 1492 on (and in the English colonies from 1619 on) would be considered an "emergency explanation." And in reality, European imperialism in India, for instance, began long before the nineteenth century. Under the British East India Company, the people of India were treated as if they were mere savages, as was noted by Edmund Burke in his impeachment charges leveled at the governor Warren Hastings, and this was done purely with the motive of exploitation and theft. Racism is a phenomenon that, in its primitiveness and irrational cruelty, appears in different guises through history unexplained by any supposedly rational thought process.