Why did an inhumane institution of course not everybody who defended it thought it was inhumane but why did that system survive, persist and grow?

为什么一个不人道的制度,当然不是所有捍卫它的人都觉得不人道,为什么奴隶制度还是会生根,发芽,成长

耶鲁公开课 - 美国内战与重建课程节选