The most important reason that Southerners sought territorial expansion was that they needed new lands to cultivate cotton. Except for a few financial downturns, prices for cotton rose throughout the nineteenth century as demand from manufacturers in the North and overseas continued to grow. For this fundamental reason, Southerners craved new, inexpensive lands and pursued them through such measures as Indian removal, which drove Creek, Chickasaw and Choctaw peoples from the fertile "black belt" in Alabama and Mississippi.

They supported the annexation of Texas for the same reason and the Mexican War, which promised even more territory. This material interest was at the heart of Southern desires to expand, undergirding such factors as nationalism and a genuine belief in the nation's "manifest destiny" to expand westward.

Some in the upper South, including Maryland and especially Virginia, hoped to expand so they could profit from the sale of their own enslaved people, whose value skyrocketed along with cotton during the nineteenth century. Some even hoped that they could sell the entire African American population of these states westward. In short, many Southerners saw in expansion both economic opportunity and political expedience. Some even hoped to spread an empire of slavery into Cuba and Central America. Slavery was at the heart of Southern support for national expansion.