Yes, at this point, our readings may seem to be repetitive, but perhaps that's the point. This chapter, from Hummel's Emancipating Slaves, Enslaving Free Men highlights the degree to which westward expansion (particularly the annexation of Mexico) reshaped the political parties in the United States.
This begs the question--is it all about money and politics? Is slavery--an institution that we undeniably regard as a social one today--only considered with regard to its economic and political ramifications?
Use examples from the text--they always make your discussion hold more water.