Southern leaders held territorial expansion necessary. Which pair of reasons carried that argument?

1. Southerners in national politics sought protection and enlargement of the cotton and slavery system. 2. Cultivating a single crop was wasteful and rapidly exhausted the land. 3. New fertile areas were therefore needed simply to keep production going. 4. The second reason was political rather than agricultural. 5. New territory meant additional slave states to offset the admission of new free states. 6. So exhausted soil and the balance of states in Congress are the pair that carried the argument. 7. Cotton output was rising, not falling, through these decades. 8. The Atlantic slave trade had been closed in 1808, long before this argument was made. _Source: An Outline of American History (U.S. Information Agency, 1990, public domain), section DEBATE OVER SLAVERY MOUNTS_