James L. Huston, Stephen A. Douglas and the Dilemmas of Democratic Equality (Lanham: Rowman & Littlefield Publishers, Inc., 2007), 143-144.
In Douglas’s view, it was popular sovereignty that enabled Manifest Destiny to operate successfully. Moreover, territorial expansion was necessary to keep the American experiment in self-government alive – his solution to a Gordian knot of democratic equality – because population pressure, now abetted by European immigration, consumed available land and ruined prospects for proprietorship….And Douglas had an awesome vision for future expansion: when the time came, the United States would have to absorb Cuba, Mexico, and Canada, and even then American expansion would not cease. His objection to the slavery controversy was that it interfered with the acquisition of new lands. If Americans kept to the principle of popular sovereignty, that interference would disappear.