These issues were especially important in the lower South, where 47 percent of the population were slaves. The upper South, where 32 percent of the po... by @wikipedia

These issues were especially important in the lower South, where 47 percent of the population were slaves. The upper South, where 32 percent of the population were slaves, considered the Fort Sumter crisisespecially Lincoln's call for militiamen to march south to recapture ita cause for secession. The northernmost border slave states, where 13 percent of the population were slaves, did not secede.