Soil was being eroded and wasted along the Eastern seaboard, and they were using up the great soils of the Mississippi Valley and over time that slave system just somehow wasn't going to work out.

东部沿海地区的土地因被侵蚀而荒废掉,密西西比河谷地区的土地资源即将被耗尽,但就在这种情况下,奴隶制依然能维持南方的经济

耶鲁公开课 - 美国内战与重建课程节选

Well Pete, you see, there was this free labor system and this slave labor system," blah-blah blah-blah.

皮特你知道,当时北方是自由劳动制,而南方是奴役劳动制",等等,等等

耶鲁公开课 - 美国内战与重建课程节选