How did the war with Mexico affect the slavery debate?

Answer 1

The major issue dealt with the Missouri Compromise line. The feeling was that if the USA won the war with Mexico there would be an effort to control all of the states of Mexico, and since they were all south of the MO Compromise line, they would all be slave states, right? Well, this is what set off people like Henry David Thoreau who spent his "night in jail" over this very issue, he refused to pay taxes to a government that would not only tolerate slavery but seek to expand it as well.

Of course the USA did not seek to control all of Mexico and in contrast to every other conquering nation in the history of mankind, the land it did take, especially California, because the USA wanted, desperately, San Francisco Bay, they paid for that land, at a fairly reasonable price.