I agree to the first person who answered
In slavery the slave was not seen as a member of society so he could not buy, what he produced was not much and the expenses to bring and keep the slaves were becoming many.
It would be difficult to keep semi-wage earners on large properties: given the availability of land, they could try other forms of life - becoming artisans, squatters and small farmers, for example - which would complicate the flow of labor to the mercantile company, in which large traders and owners .
Mexican War. The Mexican War brought Manifest Destiny almost to a close, Gadsden Purchase would finish it. With all the land though, it also brought the question of slavery back into question. An uneasy balance had been found prior, but the new open land meant that slavery had a place to expand into. The issue had never been completely handled. It was poorly bandaged up and passed along. The legislature would have to grapple once again with the issue. This time though it would lead directly to Civil War.
