No, they weren't interested in controlling the north, or forcing their culture on the north; they only wanted the sovereignty to govern themselves as free states. They weren't pro-slavery per se, they were pro-choice. Their position could be paraphrased "If you don't like slavery, don't own any slaves; just don't try to force your anti-slavery views on everyone else." Obviously, that's a ridiculous over-simplification, just as those who claim the civil war was fought over slavery choose to ignore the more central issue of states' rights/sovereignty that led to the secession of the CSA.