Why were yeoman farmers often called "the backbone of the South" in the period from 1820 to 1850?

When government officials wanted to oversee how Southern land was cultivated, yeoman farmers challenged the idea.
Yeoman farmers grew vegetables, raised animals, and made their own household products—they were very self-sufficient.
Yeoman farmers were the men who cultivated large amounts of cotton and sustained the Southern economy.
While many Southerners moved North to work in the factories, yeoman farmers remained in the South and cultivated the land.