A) A fort was established and many were killed by diseases
Lewis and Clark's expedition was not positive to the native of Mandan village the most devastating epidemic was the smallpox outbreak in the year 1837 killing a lot of people. The epidemic played an important factor in uniting the surviving Mandans and Hidatsa who later engaged in trade, farming and hunting.
The answer really depends on which of the 13 Southern states you are referring to. Each state issued their own Ordinance of Secession, in either 1860 or 1861. Hope this helps.
