Here it is not just the venerability of slavery, how old it is, but it's the idea that it has been crucial to the development of all great civilizations.

不仅仅讨论奴隶制的庄严性与历史由来,更是它曾经对人类文明的发展,起过至关重要的作用

耶鲁公开课 - 美国内战与重建课程节选