Main stream (Northern) historians often site the South’s being prevented from expanding slavery into the territories as a reason for secession. However, once the South seceded, it no longer had any claim to the territories, so their argument makes little sense. 

In 1856 there were 55 reported slaves in Kansas and by 1860 there were only two. In the Arizona territory, which includes parts of present day Arizona and New Mexico, there were less than 20.

The prospect of slavery moving west in the mid-fifties when Lincoln began exploiting the issue that made him president was non-existent. The real reason was stated by Harvard professor Charles Eliot Norton of Massachusetts. He supported the free soil movement in the West in order to “confine the Negro within the South.” 

Every time a state was admitted into the Union as a “free state” it meant two more Senators and based on population a number of Congressmen for the North. With 19 Free states and only 15 Slave states, the South was in a precarious situation politically. Congress was dominated by the industrial North and things were not going to get better any time soon with the election of a sectional president from a sectional party. 

Lincoln played on racist fears and demonized the South. That legacy survives today in the myth that the war was about the South’s desire to protect and expand slavery.