Popular sovereignty is one of the six foundational principles upon which the US Constitution is built. The other five principles are: limited government, separation of powers, checks and balances, judicial review, and federalism. Each of gives the Constitution a basis for authority and legitimacy.
Popular sovereignty was often cited before the US Civil War as a reason why individuals in a newly organized territory should have the right to decide whether or not slavery should be allowed. The Kansas-Nebraska Act of 1854 was based on this idea. It set the stage for a situation that became known as Bleeding Kansas.