Beyond even racism, what motivated southerners in their determination to expand slavery into western territories?

The defense of property rights and ability to move that property is what motivated southerners in their determination to expand slavery into western territories. Among the 34 states as of January 1861, seven slave states in the south announced their separation from the US. They formed the "confederacy" of the south. They added eleven more states although they claimed 13 states and more western territories.