Question

What is popular sovereignty

Answer 1

"Popular sovereignty" means the people are in charge of establishing a government over themselves.  

The founding fathers of the United States adopted the idea of popular sovereignty from Enlightenment philosophers like John Locke (of England) and Jean-Jacques Rousseau (of France).

The Declaration of Independence (1776), written primarily by Thomas Jefferson, asserted the concept of popular sovereignty.  The Declaration insisted that people institute governments in order to secure their rights, and that governments get their authority from the consent of the governed.  "Whenever any Form of Government becomes destructive of these ends," the Declaration of Independence said, "it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."

Answer 2

the doctrine that the people are sovereign and a government is subject to the will of the peoplea pre-Civil War political doctrine that held the individual states should decide whether to permit slavery or not.