The most likely cause of the spike in cotton production in Mississippi in the mid-1800s is the invention of the cotton gin.
The cotton gin, invented by Eli Whitney in 1793, significantly increased the efficiency of cotton processing, allowing for the rapid separation of cotton fibers from seeds. This technological advancement made it much easier and cheaper to produce cotton, leading to increased cultivation and production in the South, including Mississippi. While the growth in demand for cotton in the North and Europe also played a role, the invention of the cotton gin was a crucial factor in enabling that production increase.