What was the relationship that existed between secession and popular sovereignty?

Answer 1

The term popular sovereignty by itself does not refer to any particular issue, but in the US it came to mean the idea that the people in states or territories should vote on whether to allow slavery or not. It contrasted with the idea that geographical placement should determine which states would be slave states.

Secession refers to the act of withdrawing from the federal union. Presumably states might want to secede for various reasons, but the maintaining of slavery was the issue that provoked the actual secession of the Southern states which led to the Civil War.

So, the relationship between these two terms was that in the US, they both were proposed ways of settling the slavery issue.