How did western expansion contribute to the secession of southern states, including south Carolina

In 1860, after the republican party was created, the slavers as a declaration of war, determined the separation of the State of South Carolina from the other States of the Union. This was an act that was also followed by other States. After the war was over, the Congress declared, by constitutional amendment, that the Union among all the North American States is unbreakable, and, in addition, slavery was definitively abolished in all of them. The western expansion contributed with the Louisiana Purchase and the Lewis and Clark Expedition, which moved citizens from the south to states such as Arkansas and Oklahoma.