stoweboyd:

The Missouri Compromise of 1820, which allowed Missouri to enter the union as a slave state but otherwise forbade slavery above the 36th parallel, effectively drew the lines for the sectional battle to follow. (via A Refusal to Compromise? Civil War Historians Beg to Differ)

A fascinating read. I know too little of the history of the country I live in.

And yes – it was a refusal to compromise – on the part of the slaveholding states.