Some people opposed Clay because he owned slaves;

VOA: special.2009.01.22

And he began to write back, first to his fiancee who quickly became his wife, Mary, and he was really worried about all the slaves he owned.

随后他就开始写回信,首先给他的未婚妻玛丽,不久便结婚了,并且他对他所拥有的奴隶充满忧虑

耶鲁公开课 - 美国内战与重建课程节选

People who owned negro slaves wanted to take all their property -- including the slaves -- with them when they moved west.

VOA: special.2009.04.30