Final answer:
Plantation agriculture, particularly cotton production, was the most profitable economy in the Republic of Texas. It played a central role in the South's economy before the Civil War and relied heavily on enslaved labor.
Step-by-step explanation:
In the Republic of Texas, the most profitable economy was plantation agriculture. Large plantation operations took advantage of economies of scale, which smaller farms could not. Plantation agriculture, especially cotton production, was highly competitive and profitable, and it played a central role in the South's economy before the Civil War. The South's dependence on cotton and enslaved labor led to its economic success.