If we had to put our finger upon the year which marked the beginning of modern race relations we should select 1493-94. This is the time when total disregard for the human rights and physical power of the non-Christian peoples of the world, the colored peoples, was officially assumed by the first two great colonizing European nations. Pope Alexander bull of demarcation issued under Spanish pressure on May 3, 1493, and its revision by the Treaty of Tordesillas (June 7, 1494), arrived at through diplomatic negotiations between Spain and Portugal, put all the heathen peoples and their resources-that is to say, especially the colored peoples of the world-at the disposal of Spain and Portugal.
This, then, is the beginning of modern race relations. It was not an abstract, natural, immemorial feeling of mutual antipathy between groups, but rather a practical exploitative relationship with its socio-attitudinal facilitation-at that time only nascent race prejudice. (Loc. 8548)
[S]ocial intolerance, which attitude may be defined as an unwillingness on the part of a dominant group to tolerate the beliefs or practices of a subordinate group because it considers these beliefs and practices to be either inimical to group solidarity or a threat to the continuity of the status quo. Race prejudice, on the other hand, is a social attitude propagated among the public by an exploiting class for the purpose of stigmatizing some group as inferior so that the exploitation of either the group itself or its resources or both may be justified. (Loc. 10083)
Source: Caste, Class, and Race