Here's why:

* The South included vast territories: The South encompassed states like Alabama, Mississippi, Louisiana, Florida, and Texas, all of which were vast in land area.

* Western Expansion: The United States was expanding westward, and much of the new territory acquired (like Louisiana Purchase) was part of the South.

* The North was primarily concentrated in the Northeast: The North was mostly made up of the original thirteen colonies, which were relatively smaller in area compared to the vast Southern states.

Therefore, the South, with its expansive states and growing territory, dominated in land area in 1820.