Who became more and more hostile to the idea of slavery on moral grounds

Slavery is the major issue among the North and the South. At the beginning of the 1850s, the Northerners became more and more hostile to the idea of slavery on moral grounds, whereas slavery is sustained to be a recognized truth of life in the South. This cause led to the start of Civil War.

i really really really really really really dont know

answer; i believe the correct answer is (the willamete valley);