Williams supports this by telling how "unfree labour in the New World was brown, white, black and yellow; Catholic, Protestant and pagan" (1944: 7). It is true that many indentured white servants were taken to the Americas to work, however there were distinct differences between these white servants and the black slaves. White labour was bought for a temporary period; their freedom was theirs again once they had served their contracts. Blacks, on the other hand were bought for life. This seems to show that racist moral assumptions were being made about which types of people could acceptably be bought outright as property.
Many economic accounts discuss the profitability of slavery, for the slaveholders individually and for the South's economy but vary on their conclusions (Aitken 1971: xii). Many writers focus on the importance of slavery for the European nations involved. Adam Smith sees slavery as the basis for the industrial revolution in Britain. However this idea is also debatable. David Landes (1998) criticises this view, claiming that important advances that led to the industrial revolution (for example steam engines, mechanised wool spinning) developed independently of the Atlantic system. If theses ideas are debatable, then we must question the way they are presented as facts.
It is also important to keep in mind that no author is completely neutral. Every writer has political beliefs that are likely to influence his or her work. For example, a writer who is anti-capitalist is likely to emphasise evidence that shows the negative effects of capitalism, while a writer who is pro-capitalism would be likely to do the opposite. Slavery is a very emotive subject, Aitken says "there is a lot of suppressed guilt involved, though it is seldom permitted to show clearly through the polished academic veneer" (1971: ix). As he says it can be "amazingly difficult to filter out the ideological component" and discover what is the objective truth.