… is from pages 160-161 of Thomas Sowell’s 2008 volume, Economic Facts and Fallacies (footnote omitted):
The distinguished historian Daniel J. Boorstin said something that was well known to many scholars, but utterly unknown to many among the general public, when he pointed out that, with the mass transportation of Africans in bondage to the Western Hemisphere, “Now for the first time in Western history, the status of slave coincided with a difference of race.”
For centuries before, Europeans had enslaved other Europeans, Asians had enslaved other Asians and Africans had enslaved other Africans. Only in the modern era was there both the wealth and the technology to organize the mass transportation of people across an ocean, either as slaves or as free immigrants.